If your computer has an older OS and still has Movie Maker it is a simple option. It can't do much but it should do everything you want to do at this point, judging by what you have said in your post. Hitfilm is a free one too but it is reasonably complex so if you can't do MM you might want to try it but watch some tutorials first. It isn't simple but the tutorials should show you how to do the basics pretty well.