Because introduces a reason.
- I stayed home because I was tired.
- She left early because she had work.
- We cancelled the trip because it was raining.
Since can also introduce a reason.
- Since it was raining, we stayed home.
- Since you are here, let’s begin.
But since can also refer to a point in time.
- I have lived here since 2020.
- She has been working there since Monday.
Easy guide
Use because when you clearly mean for the reason that.
Remember that since has both a reason meaning and a time meaning.