How do I activate my free month of XBox Live Gold???

I've filled out the entire profile whille logged onto the XBox but when it gets to the membership screen, it only gives me the options to pay for "Silver (free), Gold/month, Gold/3 months, Gold/year" .

Am I missing something here?

1) What code?

2) Both of you are conflicting each other. Do I select the Gold/month membership or Silver?