How to overcome the itunes gift card code obstacle???

I'm trying to sign-in with my apple ID.....and it asks for iTunes gift card code when entering credit card details.....I have no idea what this iTunes gift card code is and how to avoid it.....in fact I do not wish to enter my credit card details.....I just want to sign in and download free s/w for now.....

Steps that takes me there

1. -->Settings

2. -->iTunes & App Stores

3. -->two options --> enter Apple ID and password

--> Create New Apple ID

4. -->I enter with my apple ID which I made from my PC....."A message comes up as "This Apple ID has not yet been used in the iTunes Store." below comes as "Tap Review to sign in, then review your account information.".....Tis is where I have two options "Cancel" or "Review".

5. -->I click on "Review" otherwise it does not allow me to sign in.

6. -->Now i am asked to enter "Country or Region" where I enter Canada.

7. -->Then I am asked whether to agree or not with the terms & conditions, I select agree.

8 -->Now to enter Billing info, I have to enter:

Payment Method: Visa, Mastercard, Amex

Payment Card: Card Number, Security Code.

Expiration date: Month, Year.

iTunes Gift Cards & iTunes Gifts: Code "This is where it asks me to enter 4 character code. what is this CODE:......?

Billing address and finally Phone.

As soon as it comes to this CODE, I do not know what to do???

Help plz....?!