To play video from a MacBook to a projector, you need to connect the MacBook to the projector using an appropriate cable, turn on the projector, and select the correct input source. Then, on the MacBook, go to "System Preferences" and select "Displays," choose the "Arrangement" tab, and check the "Mirror Displays" box. Open the video, make it full-screen, and play it. The video should now appear on the projector screen. If you encounter any issues, refer to the user manual or seek assistance from technical support.