Once you get your first badge go downstairs in a Pokemon Center and you'll get the Pal Pad, which tells you your Friend Code and you can register other people's Friend Codes so you can trade with them. The GTS (Global Trading Station) will also be open in Jubilife City now, but to get a Pokemon from there you must have seen it (it'll show up on your Pokedex). You can also deposit one Pokemon and ask for another in return (but again, it has to be on your "seen" or "own" list).
Oh, if you still want a Chimchar, PM me. I can help walk you through trading with friends. It was really confusing for me at first, but I caught on quick! :)