Videos from .mov to .mp4 format?

I recorded some videos on my iPhone that I transferred to my iPad. After a really long time, I was finally able to get them on my computer, but they won’t play. I need something that can change the format (at least that’s what I’m thinking), and I’ve installed several different programs, but I’m finding that none of them are working. The main issue is, the .mov videos won’t even open using that program.
What can I do to make my videos play on the computer, and convert them to a format that will allow me to transfer them to another device if I wanted?
Please and thank you!