What is a Chess Clock?
A chess clock is basically a device used to count, and keep track of, how long each player is thinking during a chess game. Each side has its own timer, and once you make a move, you hit the clock to stop your own timer and begin counting for your opponent.
Nowadays, modern digital chess clocks, including our online version, bring extra options like time increments (Fischer mode) and delay periods (Bronstein mode) so the whole thing stays fair for time based games. Honestly these settings matter a lot whether you are in a tournament setting or just playing casually online.