Not a problem. So! First of all, you'll encounter ledges. They can be jumped over to go down, but not climbed over to go up, and no one is quite sure why. Secondly, you're likely to encounter trees with berries growing on them. These are not safe for people to eat, they will make us sick, but Pokemon can eat them just fine. So, if your new friends need a little snack and there's a berry tree in the area, they're in luck.

You're also definitely going to encounter other Pokemon once you leave town, usually in the tall grass. The partner you've been given can protect you from them should they decide to attack.