How do I authorize my macbook for auto downloads.?

My past purchases appear and I am able to access my account but when I click and play a song it's a "quip." I can not figure out how to authorize my macbook on itunes. I did go to itunes>preferences>store> and when I check the music,app,etc boxes and click ok as directed it keeps saying I have to authorize this mac on my itunes account to enable aoutmatic downloads. I went into my itunes account and it states zero computers authorizes and there is no option there to.

Also when I did click store in itunes the option to authorize this comp didnt appear? HELP.