Hi LR Sue has given examples where these words are used to show physical location, such as 'walk through a doorway', or 'the flowerpot is by the window'. but here are a few other uses where there is no significant difference in the meaning: You can learn by example or through example You can reach your destination by reading a map or through reading a map. You can leave the room by the door or through the door. Strangely, you can only go from one floor to another by the stairs, not through the stairs! Effectively, in this type of context, they both have similar meaning ie 'using the method of...'

but things move through other things, they don't stay still there.

By is next to and through is between, silly example, my letter Y is by the * (**Y) my letter Y is through the * (*Y*)