If the student clicks PLAY, they will be taken to the GAMES page where the Wordchain they have been assigned will have a blue PLAY button under it. Clicking that will start them playing Wordchain:
Note: the first time, a progress bar will appear as Wordchain downloads/caches. Depending on bandwidth, this may take some time. In subsequent visits, the progress bar should only appear for a second or two before the game begins.
There are more support documents on the Support page. You may be interested in: