1. Insert the U disk into the USB interface of the computer and wait for the computer to recognize it automatically. If there is no automatic pop-up window, you can open "this pc" to see if the USB flash drive has been recognized.

2. Open the USB flash drive and find the MP4 video file inside. If you are not sure which video files it is, you can check the file extension, usually .mp4.

3. Double-click the video file to be played, and you can play it with the video player pre-installed in the computer. If the computer does not have a pre-installed video player, you can download and install it online, such as VLC player, PotPlayer, etc.

4. If you want to copy the video file to your computer, you can select the file to copy, then right-click and select Copy. Open the folder to be pasted in the computer, right-click the blank space and select Paste to copy the video file to the computer.

5. After playing, remember to turn off the video player first, and then take out the USB flash drive safely to avoid data loss or damage.