Amuse-toi !
It is "pon". Example: Pon la silla en la mesa. "Put the chair at the table".
(Tu) Entiendes
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It is already a negative tu-form polite command: No me digas el precio.No me di el precio - informal, impolite
to open the door -> ouvrir la porte For a command, change the infinitive "ouvrir" to either "ouvre" (tu form) or "ouvrez" (vous form).
Positive command: "come", negative command: "no comas".
The command form of the French verb "aller" is "va" for informal singular, "allez" for formal singular or plural, and "allons" for informal or formal plural. The command form of the French verb "dire" is "dis" for informal singular, "dites" for formal singular or plural, and "disons" for informal or formal plural.
This can be a little confusing. The form you are speaking of is "sé", which is identical to the first person indicative. To tell the difference, you must have context.
Où-es tu?
It is the "tu command" meaning, "Do this!"
Escucha --- listenEscuchas --- You listen