IE=Internet Explorer. A web browser. If you click on a blue “e” to get to the internet, you’re using Internet Explorer.
It starts and stops because it’s buffering. It needs to download the video from the internet. Most video websites will show you how much is buffered, by having a different colored section on the progress bar (Like for youtube, unbuffered is white, if it’s buffered, it’s a light red. And the sections you’ve already watched are the dark red).
To avoid all that stopping and starting, don’t bother watching the video until you see it’s fully loaded.