If you want to indicate the starting date or duration of an action which is still going on in the present, you can use the preposition depuis + a time expression. In English, depuis can mean two different things: “for” or “since”. When depuis is followed by a length of time, it indicates duration and is translated into English by “for”:
Jeanne étudie l’anglais depuis un an. Jeanne has been studying English for a year.
When depuis is followed by a date or a point in time, then it indicates the starting point and is translated by “since”: