What Is Their Main Difference?
Talking about Starting Points
Both prepositions are used to refer to the starting points of actions and events. The distinction is in the state of actions.
'Since' talks about actions and events that started in the past and are still happening now.
'From' talks about actions and events that started and finished in the past. For example:
He has been living in New York
He lived in New York
With Other Prepositions
'From' is usually followed by a preposition to indicate the finishing point of the time period. 'Since' is usually not followed by another preposition. Have a look:
She was our teacher
She has been our teacher
As you saw in the earlier examples, 'since' can be used with perfect tenses while 'from' can be used with all tenses.
Are They Interchangeable?
They are not interchangeable. The two may refer to a specific time period, but replacing them with each other will take away the meaning and confuse the audience.