Video editing is another job that’s probably not best suited to mobiles, but there are app options available.
On iOS, iMovie (https://apps.apple.com/us/app/imovie/id377298193) is a sound editing option and free to install and use. An option available for Android users as well as those on iOS is FilmoraGo (https://play.google.com/store/apps/details?id=com.wondershare.filmorago and https://apps.apple.com/app/filmorago-free-video-editor/id1019382747) which allows you to edit simple videos.
On your desktop or laptop computer, OpenShot (https://www.openshot.org/) is probably the easiest to use video editing app on any platform. That said, for Mac users, iMovie is arguably just as easy to use and comes ready installed.
If you’re already very accomplished with video editing and need something more powerful, the free version of Davinci Resolve (https://www.blackmagicdesign.com/products/davinciresolve/) may appeal to you. With its steep learning curve, it’s probably best to steer clear of if you’re just starting out with video.
While there are online video editing options, considering the large file sizes involved, it’s only really an option for those with very fast internet. It may give you the flexibility to work on a file from several machines, but other than that I can’t personally see any great advantage from using an online option rather than downloading OpenShot.