MP4 files are currently the most popular video file format. Both commercial and free applications can be used to edit them. Below is a brief list with links to free video file editors, ranging from simple to more advanced options:
Article with descriptions of the 10 best free video editing applications:
http://www.benchmark.pl/testy_i_recenzje/najlepsze-darmowe-programy-do-edycji-wideo.html
Free program “Easy Movie Maker” for Windows 10:
https://www.microsoft.com/en-us/store/p/easy-movie-maker/9nblggh626qk
Free program “Movie Maker: Free Video Editor” for Windows 10:
https://www.microsoft.com/en-us/store/p/movie-maker-free-video-editor/9nblggh4wwjr
Free program “Movie Maker” for Windows 7, Windows 8, and Windows 8.1:
https://support.microsoft.com/en-us/help/14220/windows-movie-maker-download
Partially free professional video editing software for advanced editing - DaVinci Resolve - HIGHLY RECOMMENDED (we use it!):
https://www.blackmagicdesign.com/pl/products/davinciresolve
Online website where you can perform basic video file operations without installing any software on your computer. The application works in a web browser:
https://online-video-cutter.com