Let's make the ship shoot bullets. Notice that we simply test for the Shift key to be down, and launch a "laser" object. Then we destroy the "Laser" object when it gets out of the playfield.

We now have to create the aliens. We are going to use the counter we dropped for this purpose: when the counter is greater than zero, we create an alien ship that we position randomly in the playfield. And subtract one to the counter. Every 10 seconds we reset the counter to 6.

When the player's bullet collides with an alien, the alien is destroyed. This can be done very simply in one event, starting with collision detection.