Buffering is typically an indication that your internet connection is not fast enough to stream the video and play it back at the same time.
Try adjusting the video quality by selecting “Auto” in the quality menu if available. (not shown on all devices) This will allow the player to select the best quality video file to stream. If “Auto” is not available, switch to one of the lower quality options.
Also ensure there are no other devices connected to your internet connection that might be slowing down your connection.