How does createProxyImpl work in ProxyFactory Contract?

Question

function createProxyImpl(address _target, bytes _data)
    internal
    returns (address proxyContract)
{
    assembly {
        let contractCode := mload(0x40) // Find empty storage location using "free memory pointer"

        mstore(add(contractCode, 0x0b), _target) // Add target address, with a 11 bytes [i.e. 23 - (32 - 20)] offset to later accomodate first part of the bytecode
        mstore(sub(contractCode, 0x09), 0x000000000000000000603160008181600b9039f3600080808080368092803773) // First part of the bytecode, shifted left by 9 bytes, overwrites left padding of target address
        mstore(add(contractCode, 0x2b), 0x5af43d828181803e808314602f57f35bfd000000000000000000000000000000) // Final part of bytecode, offset by 43 bytes

        proxyContract := create(0, contractCode, 60) // total length 60 bytes
        if iszero(extcodesize(proxyContract)) {
            revert(0, 0)
        }

        // check if the _data.length > 0 and if it is forward it to the newly created contract
        let dataLength := mload(_data) 
        if iszero(iszero(dataLength)) {
            if iszero(call(gas, proxyContract, 0, add(_data, 0x20), dataLength, 0, 0)) {
                revert(0, 0)
            }
        }
    }
}

I know the code is supposed to deal with some external contract. However, I am not able to understand the flow as well as the implementation. Can someone explain?