I think it is a good idea to read some pages in the manual. If you have a download version, you must download a .PDF-document, after being registered at Magix.
You must start in Edit modus and open the project.
place the cursor at the point you want to 'cut', click (right about the movie in the timeline) it should place the orange arrow/line at the spot. click on the little 'razor blade looking button'. should cut it, do the same at the next point, delete the sections in between you dont want.