The aim of the game is to make students practice making correct and long sentences in English. (ESL)
How to play it? As you play the game with a partner (as you would normally play tic tac toe),  make a sentence that starts with the first word you mark with a circle  or a cross sign. Then add each next word you stand on to your sentence.
Eg. if you stand on the word “school”, you can start a sentence like:
“I love SCHOOL....” , then you stand on “never”, so you need to include it in the rest of your sentence - e.g.: “I love school, even though I NEVER understand...”  - then leave the sentence open and wait for your turn to be able to make it longer or finish it with the last word you stand on when the game is over.

Your opponent does exactly the same thing.