Well, Pokemon battling is just something that's done here. It's quite popular here to battle one's Pokemon against those of other people.

It's also how you raise them! I don't battle too terribly much myself, but the Pokemon seem to like it well enough. They grow stronger the more one battles with them and some even change into a different Pokemon once it's gotten strong enough!

I believe there should be a book in the bag you were given. It may be able to explain things better than I can.