There’s one of Steinberg’s own videos here, the online help is all here, and you might also ask over in the Cubase forums where you are likely to get more responses. If you add the details of which version of Cubase you’re using to your signature, it would help people to offer more targetted advice. You might also title your post something like “How do I create a 4 or 8 bar loop from a live drum recording?”