Indeed, as Lilith said, there is no set way to make a game. You take a concept and your programming skills and put them together!
For instance, there is one tutorials, Dark Invaders I think it's called, that "scrolls" up. Isn't a sidescrolelr pretty much the same, except going sideways? Once you learn how to manipulate 2d images with Dark GDK, you'll have a good idea how to apply concepts to what you want to do.
Also, make sure you check out the normal DarkBASIC Pro tutorials. There are alot more of them, and it is a pretty simple process to convert them to DarkGDK.
Cheers
Tux is my guildmaster.