1. Open iTunes on your computer.
2. Connect your iPhone or iPad to your computer using the USB cable that came with it.
3. Click on the "Device" icon in the top left corner of iTunes.
4. Click on the "Videos" tab in the left sidebar.
5. Drag and drop the videos that you want to transfer from your documents onto the iTunes window.
6. Click on the "Sync" button in the bottom right corner of iTunes to start transferring the videos to your iPhone or iPad.
Once the videos have transferred, you will be able to watch them on your iPhone or iPad by opening the "Videos" app.