The players look like circles.
The red player is the tagger, or, IT. The blue player(s) aren't taggers.
If you touch a player, and you are IT, then the player you tagged becomes the tagger.
You can move by moving your mouse cursor.
Recommendations
I recommend you play in full screen, because if your mouse moves outside the window, your player stops moving, because JavaScript can't detect mouse movements outside of the window.
Playing with just yourself is sort of, boring. If you get in and nobody's online, then maybe you should ask your friend(s) to play with you!