You have already made them a Buddy, judging by your question, so all you need to know now is that each Buddy can get one gift from you a day. On top of that there is a limit to howmany gifts oyu can give in a day (I think it's 5). On top of those 5 you can get extra gifts to give (but still holding to the 1 per recipient per day limit) when you get trophies from leagues and if you are in a gang and the gang completes the gang challenge.
That's how many, but to actually give just look at their avatars you Buddy list at the bototm of the screen and if they have a flashing XXX (black Xs on red square background) then they are available to be given a gift. Be aware that the update on numbers, etc. is not immediate so you may click on what you thought was a valid target only to see thier profile pop-up instead. All that means is that you've hit your gift giving limit and you were a bit too quick on the last try :)
