Each Pokemon has a type. [ She tilts her screen sideways; there's a Munna floating lazily nearby, sleeping. ] For example, my starter is a Psychic-type...it basically tells you what their attacks might be imbued with, and what they're strong and weak against. In the games, you could choose from a grass, fire, or water starter. Grass was weak to fire but strong against water; water was weak against grass but strong against fire; fire was strong against grass but weak to water. Learning type effectiveness is key to becoming a good Pokemon trainer.

For example, the first gym is a flying-type gym...so knowing that, I've trained up electric-types.

[ She's still perfectly happy to play Pokedex, apparently. ]

Gyms are in some of the cities in the region...there are eight in Johto in all. They're run by "leaders", whom are trainers of exceptional talent. When you defeat a gym in battle - that is, the leaders as well as their minions - you get a badge to prove you did so, and prize money, and TMs or HMs, which teach your Pokemon special moves. When you get all eight, you're supposed to be able to challenge the Elite Four, who are even higher level...