Most smartphones have native "merge" or "movie" features that don't require downloading new software:
Open the iMovie app , tap Start New Project , then select Movie . Choose your clips (like "IMG_0124.MP4") from your library and tap Create Movie . IMG_0124MP4
In your Gallery app, long-press to select multiple videos, tap Create , and select Movie . This will automatically arrange them on a timeline for editing. Most smartphones have native "merge" or "movie" features
To "put together" video clips like "IMG_0124.MP4" into a single feature or movie, you can use built-in tools on your phone or popular third-party apps. Built-in Options tap Start New Project