After the introduction, where you see the city is under attack and when Wily escapes, you will proceed to the right. This stage has a few enemies and jumps, but does have two bosses in succession.
In the first screen, you will encounter two Bunby Tank (which splits into a slightly more aggressive Bunby Top if the base is damaged), and a Metall (which frequently hides within its helmet.
One screen past this is the first boss of the game, the Mad Grinder. It knows three moves: the first being the forward and backward movement, and the second is using a short upward jump. It will also launch a projectile from its head which travels forward along the ground, then returns by moving up and to the right.
It is best dodged by moving close to the grinder just before it makes the attack. It is vulnerable to shots to the head, and begins to smoke as it takes damage. When destroyed, you can continue to the right.
Before you reach bass, you will need to jump over a few pits, past the wrecked enemies.
When you reach his location, he will warp in. As an introductory challenger, he will only fire a single shot, and try to jump attacks. When either you or Bass is low on health, the battle will stop (with a different dialog depending on the victor). After they warp out, you will exit the stage as well.