I've loaded a video in Movie Maker, edited it to the parts that I wanted and then I exported it into a MP4.

There are parts that are missing in the MP4 and there are parts that are within the MP4 that aren't in the Movie Maker file that I thought I edited out but they are still there. Why is this?

The Movie Maker file is exactly what I want but once I export it to MP4, the video has different parts?

Why is this?