I have redeemed a gift, if I buy an app will the money come off my account or from the gift card, and how will I know where it's am off?

If you are sending a gift (based on the page that you posted from), then your credit card will be charged - you can't gift from your account's balance.

If you are buying for yourself then it should automatically come oout of your account's balance. From http://support.apple.com/kb/HT5582 :

When making purchases, content credits are used first, followed by Gift Certificate, iTunes Card, or Allowance Account credits; your credit card or PayPal account is then charged for any remaining balance.

The only way to know for sure how you've been charged is to check your account's balance before/after a purchase and/or your credit card, there isn't anywhere on your account that says how a particular purchase was made.