The post ahead of you will have two words that fit a stated theme. Example:
Types of fruit:
Apples, Oranges, _______
You might then answer:
Apples Oranges, Grapes
THEN you use your last word there [*grapes*] and start a new "Triplet", fitting grapes into a new theme for the next set. Like:
Ingredients used to make wine:
Grapes, Pears, _______
The next person might answer:
Grapes, Pears, Dandelions
... and then post:
Types of Plants:
Dandelions, Roses, _______

The major idea is to finish one "Triplet" and then start a new one using the same word (in a different thematic way). Themes can vary wildly, of course. And (just a heads-up) ... making the game too difficult and/or obscure, especially at first, will stop it dead in its tracks before it even gets 'legs'. *Challenging* is great. *Confounding* is the best way to kill a game in a hurry!