ISNEW() will check if the formula you create is running when a new record is created and will return TRUE if it is. If the record is being edited, the function returns FALSE.
ISNEW. Description: Checks if the formula is running during the creation of a new record and returns TRUE if it is. If an existing record is being updated, this function returns FALSE.
It Checks if the formula is running during the creation of a new record and returns TRUE if it is. If an existing record is being updated, this function returns FALSE.