Q: How to used gift card

This might help:

iTunes Store: How to redeem a code

If you scratched off part of the code, and can not read it: Invalid, inactive, or illegible codes

Ignore.

Are you telling the OP to ignore me ?

No, of course not.

I posted the link on how to redeem a card but we posted at the same time so I just deleted it.

Oh, another one of those times where I have mis interpreted what I am reading on the screen

No problem 

if i have 14.00 on my account, but want an app that is 14.99 can the 14 be taken from account and the rest off my credit card associated to my appstore account?