Based on blog http://www.iteggs.com/2016/10/18/are-it-pointclick-admins-turning-into-it-developers/

PowershellSnippedCS.ps1

#The C# Code starts with @ sign and ends with @ sign.
$CSharpCode = @"
public class ExampleCSharp
{
    
    public string ReturnTheString(string returnString)
    {
        string Combine = "Your awesome text is : " + returnString;
        return Combine;
    }
    
}
"@

#Add the C# code as definition
Add-Type -TypeDefinition $CSharpCode

#Example is the public class
$ExampleCSharpCode = New-Object -TypeName ExampleCSharp

#Run the public string ReturnString to get the results
$ExampleCSharpCode.ReturnTheString("Hello World")