can't download free apps

Why not? What issues are you having? What is it doing? Saying? Anymore information you have would help.

If you already created your Apple ID, you will have to enter a credit card in order to verify your account. No charges will be made on the card, it just has to be active. You can then Re-enter your account and remove the credit card by changing the type to NONE.

If you have not set up an Apple Account yet, you can follow these steps to properly set up an iTunes Account without a Credit Card.