Get him or her checked out...you may want to keep them secluded to one room or area for now, they will probably want to hide if they aren't very socialized and they can get stuck or hide sometimes in the tiniest and worst possible places.
Canned food, cat sip (cat milk) will bring them out of hiding and help with the initial bonding. Watch out, even a wee one can give you a nasty bite when they're scared.
If you decide to keep him or her, make sure to get them fixed promptly, if not a male will start spraying and a un-altered female can spray as well, not to mention how often they can come in heat.
My fur babies are indoor only because of location, other ferals, and predators (dogs, and wild coyote).
I have one cranky female that knocks stuff off of shelves, talks back if you tell her "no", does sneak attacks, and bitch slaps the other for no reason other than he exists...and then in the next moment she can be the sweetest thing you've ever seen showering you with love.
The male is easy-going and laid back and thinks he's a dog, he wags his tail and will lick you all over. He cries like a baby if I'm outside too long and he always seems to know when I'm upset or not feeling well.
Don't know what I'd do without them some days.
.
phobia.