Hello marydolan1, welcome to the Microsoft community, my name is Luiz Cruz, an independent consultant and I would be happy to help you.
To edit mp4 videos on Windows 10 you can use the "Video Editor" program that is already pre-installed on the system;
If you are unsure of how to use it, I recommend that you follow the instructions provided in the link below:
https://www.howtogeek.com/355524/how-to-use-win...
Note: This is not a Microsoft website but appears to be providing accurate and secure information;
I hope I helped, see you soon!