Use of a USB microphone is possible with Cubase. I would even call it easy, but that’s a very unusual rig to use for music production, so your expectation that Cubase should be optimized for this unusual situation is unreasonable.
Note that there are DAWs that are optimized for the limited kind of gear you are using. For example, GarageBand. I would highly recommend you look into using that instead of Cubase.
Otherwise, if you are finding this basic step to be difficult, I’ll warn you there are many more steps ahead of you in Cubase that you may find equally difficult and frustrating. Using something simpler, like GarageBand, will avoid many of those issues and may be a better choice for you than Cubase.