Click the play button to play the video when the video has loaded. Most of the time you need to close the ads before you play the video (The close button looks like 'x'). Some video host don't allow adblock, you have to disable adblock, such as 'openload'. If the video doesn't load, refresh the page and try again.
If the video still doesn't load, click 'Direct Link' to watch the video. If above ways do not work, try to use other browsers. The best browser to watch videos online is Google Chrome. If the video keeps buffering, Just pause it for 5-10 minutes then continue playing.