What Is Their Main Difference?
The main difference between 'by' and 'before' is that 'before' is used to show a time in advance of a certain time while 'by' talks about a time that is not later than a given deadline.
Talking about Deadlines
We can use 'by' to set deadlines. We use 'by' to set a specific time in which everything must occur before or at the exact moment. For example:
Turn in your assignments
Talking about Earlier in Time
We use 'before' to show that something occurred in advance of a particular time or event. We do not use 'before' to set a deadline but we just use it to set a time. For example:
Try to be here
He always arrives
Talking about Location
Both 'by' and 'before' are used to show location. 'By' is used to show the specific location of something near a place or another object.
'Before' is used to show the location of something in front of something else. For example:
I always go on picnics with my friend
They killed him right