Click on Variables in the Code tab, then click on Make a Variable.
Type in the name of your variable. You can choose whether you would like your variable to be available to all sprites, or to only this sprite. Press OK
Once you have created the variable, it will be displayed on the Stage, or you can untick the variable in the Scripts tab to hide it.

Can you keep track of the player’s score? Players should score points when they click on ghosts to catch them.

Each time a player clicks on a ghost, their score should increase.