A like is a quick and friendly way to let a video owner or creator know that you value and appreciate their video. To like a video, just click the thumbs up button located at the right hand corner below the video player. Its value will increase and turn from grey to black color to signify that your like has been registered.
You can unlike a video by clicking on the thumbs up icon at the bottom right hand corner of the video player again, or by clicking the thumbs down button at the right hand side below the video player. you can access your liked videos by clicking the liked videos tab from the left sidebar. You can also navigate to your likes page from your profile.