In order to be able to perform an operation (e.g. copying & pasting or deleting) on just an individual segment of one consistent piece of video, you need to chop up that piece of video into several objects first. The key to all of this is the split function that you can reach via the hot key "T" on your keyboard. Make sure to edit your arrangement in timeline mode. Place the play cursor at the beginning of the segment that you want to cut/copy or delete. Press "T" on the keyboard. You will see that the consistent video object now gets cut up into two video objects at the cursor position, both of which can be manipulated separately from now on. Now, position your cursor at the of the desired segment and press "T" again. Another cut will be placed and you will end up with three objects. You can select the segment in the middle separately and copy or delete it now. Once you get the hang of using the split function to chop up objects in Magix video editing programs into separate objects, you will probably understand pretty intuitively how you can utilize this in your editing process and what technical and create possibilities this offers to you.