Above.

I've seen a few bits on Google but they're so old the links don't work.

Can anyone help? I'd rather print out the code and stuff than follow a YouTube tute.

https://github.com/KaanAlpar/space_shooter_tutorial

This might not seem like what you're looking for but I promise you that the principles are the same, the only real differences in the code comparing this to space invaders would be space invaders have their enemies move in patterns rather than completely random but of course there's no rule to say you can't mix things up.