This is the 4576th most frequent French word.
mettez
"Put" or "place" (imperative form of "mettre").
The verb 'mettez' is used here as an imperative form of 'mettre' (to put), addressing someone formally.
Mettez le livre sur la table.
Put the book on the table.
Here, 'mettez' is in the present tense indicating an action of putting something on, and used in a formal context.
Quand vous mettez le manteau, vous serez plus chaud.
When you put on the coat, you will be warmer.
In this sentence, 'mettez' is used as part of the reflexive verb 'se mettre à' (to start doing something), in imperative form addressing someone formally.