How do I trim my video?

• iPhone or iPad
  • Launch the Photos app on your iPhone or iPad.
  • Tap on the video you'd like to edit.
  • Drag the left and right anchors in the top bar so the section of video you'd like to keep is within them. The left anchor lets you choose the start point and the right anchor lets you decide where the video clip will end.
  • Tap the Trim button in the upper right hand corner.
  • Tap on either Trim Original or Save as New Clip — the second option preserves the original video and creates a new file for your trimmed version. 

• Android Devices
  • Open the Gallery app on your Android mobile device.
  • In the Gallery, choose the video you wish to edit.
  • From the playback screen, tap the three dots in the upper-right corner, and select “Trim” from the dropdown menu.
  • Use the trim selectors on the playback timeline to adjust your video clip (The left selector lets you choose the start point and the right selector lets you decide where it will end).
  • When you’re finished trimming your video, tap “Save”.
  • The app will prepend your video filename with “TRIM_(filename)”.
  • A pop-up will ask you to select a player app to view your new video. Select the app you are most comfortable with to view your shortened video clip.
  • If you don’t want to open the video in the video player, you can simply cancel out of the operation and share your shortened video to the service or location you desire.
  • http://www.howtogeek.com/201843/how-to-trim-and-cut-videos-on-your-android-device/

• Samsung Devices
  • Open the Gallery or Videos app on your Samsung mobile device.
  • Select the video you wish to trim.
  • Once the video opens, tap the three options dots in the upper-right corner then tap Edit -> Studio -> Video Trimmer.
  • Use the yellow marker to advance the video to where you want your clip focused on.
  • Use the selectors to pick your start and end points (The left marker lets you choose the start point and the right marker lets you decide where it will end).
  • When you’re finished, tap “Done”.

A popup will appear asking you name your new video. Unlike Android, Samsung doesn’t automatically save the new file, so you will have to give it a filename, and then tap “Save”