Full template of a contract that can flashloan from Aave. You also need to add your own logic in terms of what you want to do with the lent amounts in the executeOperation function

MyFlashLoan.sol

pragma solidity ^0.6.6;

import "https://github.com/aave/flashloan-box/blob/Remix/contracts/aave/FlashLoanReceiverBase.sol";
import "https://github.com/aave/flashloan-box/blob/Remix/contracts/aave/ILendingPoolAddressesProvider.sol";
import "https://github.com/aave/flashloan-box/blob/Remix/contracts/aave/ILendingPool.sol";

contract Flashloan is FlashLoanReceiverBase {
    constructor(address _addressProvider) FlashLoanReceiverBase(_addressProvider) public {}

    /**
        This function is called after your contract has received the flash loaned amount
    */
    function executeOperation(
        address _reserve,
        uint256 _amount,
        uint256 _fee,
        bytes calldata _params
    )
        external
        override
    {
        require(_amount <= getBalanceInternal(address(this), _reserve), "Invalid balance, was the flashLoan successful?");

        //
        // Your logic goes here.
        // !! Ensure that *this contract* has enough of `_reserve` funds to payback the `_fee` !!
        //

        uint totalDebt = _amount.add(_fee);
        transferFundsBackToPoolInternal(_reserve, totalDebt);
    }


    // Rest of your code goes here
    
    /**
        Flash loan 1000000000000000000 wei (1 ether) worth of `_asset`
    */
    function flashloan(address _asset) public onlyOwner {
        bytes memory data = "";
        uint amount = 1 ether;

        ILendingPool lendingPool = ILendingPool(addressesProvider.getLendingPool());
        lendingPool.flashLoan(address(this), _asset, amount, data);
    }
}