Pokémon XD: Gale of Darkness/Pokémon Lab Headquarters

When you start a new game, you'll first see an opening. After that, write down your name. You'll now be forced into a battle.

This is an easy fight. You'll have a Lv50 with the moves Earthquake, Dragon Dance, Brick Break, and Dragon Claw, and your enemy is a Lv50. Defeat the Metagross with two Earthquakes as only this move is strong on him.

Watch the short scene. You'll find out that you were just in a battle simulator. First, get used to the controls and to check your starter Pokémon,. It'll have four attacks: Tackle, Tail Whip, Bite, and Sand-Attack and will be at level 10.