Mail. Some people still use it.

Not until you learn English.

Is this actually a friend or someone you met online?

If it is some random person you friended on social media, read WT Door's answer, including the links.  This is a scam.

If this is actually someone you have met in person and know well, sure.  Put it in the mail and send it to their APO/FPO address.  

Yes.  But your friend probably won't be able to use it if it's for the Olive Garden or Red Lobster.

A gift card from where?