by

near or next to.

Example: The mailbox is by the bus stop.

at some time before (the given time).

Example: Be back by ten o'clock!

if something is done by somebody, it is done through their action

Example: The matter was decided by the chairman.

if something is created by somebody, they are the creator, author, etc.

Example: There are many well-known plays by William Shakespeare.

shows how someone does something

Example: I avoided the guards by moving only when they weren't looking.