Mode Gerund
The gerund mode is impersonal that is to say that it is not preceded by the pronouns "je", "tu", "il", "nous", "vous" and "ils". Its particularity is to be preceded by "en" in its formation.
The gerund is used to express the circumstances of the action expressed by the main verb. This is the ideal time to introduce a circumstantial complement. It allows to be able to designate the verb as an adverb while keeping its verb properties.
C'est en forgeant qu'on devient forgeron.
A correct language means that the subject of the gerund is the same as that of the main verb. So we do not say "En attendant, veuillez agréer..." but "En attendant, je vous prie d'agréer...".
Mode Gerund
There are two tenses in this mode: present and past.