Simply click the slot where you want to play. The starting player alternates, but you start first if you lose. You can find some brief explanation about its structure and how it works in the project.
You may ask yourself why is this called "Tiny TicTacToe", this is the smallest efficient version I've implemented of TicTacToe in scratch! It only has 1 script, using 2 variables and 3 lists Have fun!