The same way you do in every other Pokemon game fight other Pokemon.
or you can put them in daycare, I currently am levelling up empoleon and torterra in daycare training infernape with an exp share and actually killing stuff with my luxray all the while walking around with an egg.
Chat with our AI personalities
his level 47
You can't, idiot.
It's hard without cheating for rare candy so you need patience
it depends on the Pokemon that are evolving
It evolves at level 40.