This ARM template shows how to use conditions and logical/comparison functions to dynamically create windows/linux for prod/non-prod

vmCondition

{
    "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        "vmNamePrefix": {
            "type": "string",
            "defaultValue": "VM",
            "metadata": {
                "description": "Assing a prefix for the VM you will create."
            }
        },
        "production": {
            "type": "string",
            "allowedValues": [
                "Yes",
                "No"
            ],
            "metadata": {
                "description": "Select whether the VM should be in production or not."
            }
        },
        "platform": {
            "type": "string",
            "allowedValues": [
                "WinSrv",
                "Linux"
            ],
            "metadata": {
                "description": "Select the OS type to deploy."
            }
        },
        "userName": {
            "type": "string",
            "defaultValue": "azureadmin",
            "metadata": {
                "description": "Specify the OS username"
            }
        },
        "pwdOrssh": {
            "type": "securestring",
            "metadata": {
                "description": "If Windows, specify the password for the OS username. If Linux, provide the SSH."
            }
        }
    },
    "variables": {
        "vNetName": "vnet01",
        "subnetName": "subnet1",
        "vNetAddressPrefix": "192.168.0.0/16",
        "subnetAddressPrefix": "192.168.0.0/24",
        "vnetID": "[resourceId('Microsoft.Network/virtualnetworks', variables('vNetName'))]",
        "subnetRef": "[concat(variables('vnetID'),'/subnets/', variables('subnetName'))]",
        "windowsOffer": "WindowsServer",
        "windowsSku": "2016-Datacenter",
        "windowsPublisher": "MicrosoftWindowsServer",
        "linuxOffer": "UbuntuServer",
        "linuxSku": "12.04.5-LTS",
        "linuxPublisher": "Canonical",
        "availabilitySetName": "[concat(parameters('platform'), '-', 'avset')]",
        "availabilitySetId": {
            "id": "[resourceId('Microsoft.Compute/availabilitySets', variables('availabilitySetName'))]"
        },
        "vNicName": "[concat(parameters('platform'), '-', 'nic')]",
        "pNicName": "[concat(parameters('platform'), '-', 'pip')]",
        "vmName": "[concat(parameters('vmNamePrefix'), parameters('platform'))]"
    },
    "resources": [
        {
            "apiVersion": "2017-04-01",
            "type": "Microsoft.Network/virtualNetworks",
            "name": "[variables('vNetName')]",
            "location": "[resourceGroup().location]",
            "properties": {
                "addressSpace": {
                    "addressPrefixes": [
                        "[variables('vNetAddressPrefix')]"
                    ]
                },
                "subnets": [
                    {
                        "name": "[variables('subnetName')]",
                        "properties": {
                            "addressPrefix": "[variables('subnetAddressPrefix')]"
                        }
                    }
                ]
            }
        },
        {
            "type": "Microsoft.Network/publicIPAddresses",
            "apiVersion": "2017-04-01",
            "name": "[variables('pNicName')]",
            "location": "[resourceGroup().location]",
            "properties": {
                "publicIPallocationmethod": "Dynamic",
                "dnsSettings": {
                    "domainNameLabel": "[toLower(concat(parameters('vmNamePrefix')))]"
                }
            }
        },
        {
            "type": "Microsoft.Network/networkInterfaces",
            "apiVersion": "2017-04-01",
            "name": "[variables('vNicName')]",
            "location": "[resourceGroup().location]",
            "dependsOn": [
                "[resourceId('Microsoft.Network/publicIPAddresses/', variables('pNicName'))]",
                "[resourceId('Microsoft.network/virtualNetworks/', variables('vNetName'))]"
            ],
            "properties": {
                "ipConfigurations": [
                    {
                        "name": "ipconfig1",
                        "properties": {
                            "privateIPAllocationMethod": "Dynamic",
                            "publicIPAddress": {
                                "id": "[resourceId('Microsoft.Network/publicIPAddresses', variables('pNicName'))]"
                            },
                            "subnet": {
                                "id": "[variables('subnetRef')]"
                            }
                        }
                    }
                ]
            }
        },
        {
            "condition": "[equals(parameters('production'), 'Yes')]",
            "type": "Microsoft.Compute/availabilitySets",
            "apiVersion": "2017-03-30",
            "name": "[variables('availabilitySetName')]",
            "location": "[resourceGroup().location]",
            "properties": {
                "platformFaultDomainCount": 2,
                "platformUpdateDomainCount": 3
            },
            "sku": {
                "name": "Aligned"
            }
        },
        {
            "type": "Microsoft.Compute/virtualMachines",
            "apiVersion": "2017-03-30",
            "name": "[variables('vmName')]",
            "location": "[resourceGroup().location]",
            "dependsOn": [
                "[resourceId('Microsoft.Network/networkinterfaces/', variables('vNicName'))]",
                "[resourceId('Microsoft.Compute/availabilitySets/', variables('availabilitySetName'))]"
            ],
            "properties": {
                "availabilitySet": "[if(equals(parameters('production'), 'Yes'), variables('availabilitySetId'), json('null'))]",
                "hardwareprofile": {
                    "vmsize": "Standard_D1"
                },
                "osProfile": {
                    "computername": "[parameters('vmNamePrefix')]",
                    "adminusername": "[parameters('username')]",
                    "adminpassword": "[parameters('pwdOrssh')]"
                },
                "storageProfile": {
                    "imageReference": {
                        "publisher": "[if(equals(parameters('platform'), 'WinSrv'), variables('windowsPublisher'), variables('linuxPublisher'))]",
                        "offer": "[if(equals(parameters('platform'), 'WinSrv'), variables('windowsOffer'), variables('linuxOffer'))]",
                        "version": "latest",
                        "sku": "[if(equals(parameters('platform'), 'WinSrv'), variables('windowsSku'), variables('linuxSku'))]"
                    },
                    "osdisk": {
                        "name": "[concat(parameters('platform'), '-osDisk')]",
                        "createOption": "FromImage",
                        "managedDisk": {
                            "storageAccountType": "Standard_LRS"
                        },
                        "caching": "ReadWrite"
                    }
                },
                "networkprofile": {
                    "networkinterfaces": [
                        {
                            "id": "[resourceId('Microsoft.Network/networkinterfaces', variables('vNicName'))]"
                        }
                    ]
                }
            }
        }
    ],
    "outputs": {
        "vmEndpoint": {
            "type": "string",
            "value": "[reference(concat(variables('pNicName'))).dnsSettings.fqdn]"
        },
        "platform": {
            "type": "string",
            "value": "[parameters('platform')]"
        },
        "connectionInfo": {
            "type": "string",
            "value": "[if(equals(parameters('platform'), 'WinSrv'), 'Use RDP to connect to the VM', 'Use SSH to connect to the VM')]"
        }
    }
}

Very simple to understand examples and well explained!!

I have a question. In this example we have two options: WinSrv and Linux. And using the If we say if WinSrv then WinSrv else Linux.

But what function and how can be used for dealing with three options? So, option1, option2, option3
Can this be done without a case statement function?

@webyxdesign you can do something like this:
[if(equals(parameters('options'),'Option1'),Option1,if(equals(parameters('options'),'Option2'),Option2,Option3))]

Where options is your parameter name.
This example basically is an if, else if, else kind of conditional. if false, do an if again, and if false, do another if....
To simplify:

if options == 'Option1':
      print('Option1)
 elif options == 'Option2:
     print('Option2')
else:
    print('Option3')

can this if statement be used directly inside variables section