EN and DANS

Je fais mes devoirs en 2 heures.
I do my homework in 2 hours (it takes me 2 hours to finish).

Il a appris le français en un an.
He learned French in one year (it took him one year).

EN (for duration it takes to do something) :
- It means "within" or "in the time of".
Use "en" to express how long it takes to complete something.

Je partirai dans 10 minutes.
I will leave in 10 minutes (10 minutes from now).

Le film commence dans une heure.
The movie starts in one hour (one hour from now).

DANS (for future starting point) :
- It means "in" as in "after a delay of".
Use "dans" to express when something will happen in the future, starting from now.

Je vais finir ce projet en 3 jours, mais je vais commencer dans 2 jours.
I will finish this project in 3 days (it will take me 3 days), but I’ll start in 2 days (2 days from now).