iTunes 2 factor verification

On my Mac I wish to sign into iTunes. I put my Apple ID in then my password. It declines the password telling me to enter password with verification code. I seem to have used every combination of inputting password with 6 digit code with spaces, no spaces, code attached to the password using no spaces then with spaces, but it still won't let me sign in. What am I doing wrong.

Using iMac IOS 10.10.5 Yosemite

Best wishes and thanks guys for your expected assistance.