1. PrÉpositions avec le temps
DEPUIS, PENDANT, & IL Y A

2. The French prepositions depuis, pendant, and—far less commonly—pour each express the duration of an event a little differently, with the result that many English speakers mix up depuis and pendant and overuse pour.

3. DEPUIS
Depuis means "since" or "for." It is used with a French verb in the present tense to talk about an action that began in the past and continues in the present.

4. ExEmples
Depuis quand étudiez-vous le français ?    How long have you studied French?

5. ExEmples
   J'étudie le français depuis 3 ans.    I've studied French for 3 years (and still do).

6. Exemples
   J'étudie le français depuis    I've been studying French since 2009.

7. pendant
Pendant means "for" and refers to the entire duration of an action in the past or future, with no relation to the present.

8. exemples
Pendant combien de temps avez-vous étudié le français ?      How long did you study French?

9. exemples
J'ai étudié le français pendant 3 ans.    I studied French for 3 years (and then stopped).

10. exemples
   Je vais habiter en France pendant 2 mois.    I'm going to live in France for 2 months.

11. Pendant
Pendant followed by a noun means "during." In this sense, it is synonymous with durant.

12. exemples
J'ai vu un film pendant mon séjour.     I saw a film during my stay.
 Pendant ce temps, il m'attendait.     During this time, he waited for me.

13. Il y a…
“Il y a” means "ago" and can only be used for things that are already completed. The verb in the sentence must be in the past and il y a must be followed by some reference to time.

14. exemples Je suis arrivée il y a une heure. I arrived an hour ago.
 Il a parlé il y a 5 minutes.     He spoke 5 minutes ago.
   Il y a deux jours, j'ai vu un chat noir.     Two days ago, I saw a black cat.