Pokémon Simulator is a peculiar little utility, and is slightly more than just a game, in that you don't follow an adventure as you do in any of the numerous Pokémon cartridges.
Instead, you simply use Pokémon Simulator to reproduce the combats between different Pokémon. This makes it great for learning the strengths and weaknesses of the various characters and learning the best attacks to choose to defeat them.
Pokémon Simulator features characters from all the Pokémon that have appeared in the various editions, meaning you can train against practically anyone.
If you've never really got caught up in the whole Pokémon craze and don't know about how the game works, you'll pretty much have to teach yourself, as the game help doesn't explain the basic principles very well.
But if you're a fan of the games, Pokémon Simulator will give you an extra edge in your battles.