Heya, Silmana.
Handling uploaded videos works the same as any other file. Have a look at
this document for more info.
If you want the User to be able to upload multiple files at once, you'll probably want to extend the form using JavaScript.
here is an excellent article covering that.
To autoplay a video file, you can simply set the autoplay="true" attribute for your embed. The object tag probably has a similar attribute, but this is not my area of expertise. Try asking this question in the HTML/CSS forum.
And to remove a file, it depends on how you are storing it. If it is stored in the filesystem, a simple
unlink() call will do the trick. If it is stored in the database, you can simply use the DELETE command.