Have a pokemon that has some kind of ailment or has fainted? Then bring them here to meet Nurse Joy and her assistant Chansey they will be able to heal your pokemon back to full strength!
When you go to any poke center there is usually a PC in which you can withdraw or deposit any pokemon as long as your limit of pokeballs on your person doesn't excede six pokeballs! Each box can hold at least thirty pokeballs in each!