- a definite past time until now: She has stayed there ever since. - before the present time : He has been long since dead.
- after a time in the past : He has since become rich.
Remember, it requires a present perfect.
As to from(a preposition),it's used as a function word to indicate a starting point of a physical movement or a starting point in measuring or in a statement of limits (I came here from the city; a week from today and so on).