Both are preposition, used in different ways. 'By' is an instrumental preposition, meaning it indicates a means or mode through which something is done whereas 'From' indicates the source or starting point. Example: He came from the village in the morning. He came by bus. In the first sentence the word 'from' is used to indicate the point where movement started, which is 'the village'. In the second sentence, the word 'by' tells us of the means or mode of transport, which is by bus.

from是从…，由… by是通过