Split
It will cut the movie in half, essentially giving you two movies then - the movie before the split and the movie after. You can delete the half you don't want.
Assuming you're talking about Windows Movie Maker.
I'll take a screenshot and add arrows! BRB
Back
Pause the video and use the forward and back buttons to get to the right place where you want to cut the video. Press the "split" button to cut it.
On the play bar thing, you can right click I think on the section you want to delete and choose delete.
You can also add songs and stuff, I don't know if editing them is the same and doing videos.