By and placeWe use the preposition by to mean "near", "beside" or "at the side of".
- The man was sitting by [=besides] the window.
- There is a cottage by the sea.
By and method of somethingWe use "by" to show how or in what something is done
a) a particular method of transportby train/car/boat/plane/taxi/bus
- I decided to go by plane.
- They go to school by bus.
- I have never travelled by sea before.
- They often go to England by air.
b) a particular method of communicationby post/phone/email/fax etc
- I'll send the contract to you by post.
- They spoke by telephone.
c) a particular method of paymentby credit card/cheque
- We paid by credit card.
- May I pay by cheque?
By and timeWe use "by" to show deadlines or the end of a time period.
- Can you finish your work by tomorrow?
- The documents should be ready by Monday.
- Please send your application by ten o'clock.
By and the passiveIf we want to show who or what does, creates or cause something in the passive voice, we use "by".
- The deer was killed by the hunter.
- Who was this house built by?
- I was hit by a car.
By and -ing formWe use by +ing verb to show how something is done.
- Turn on the heating by pressing this button. [=Press this button to turn on the heating.]
By and reflexive pronounIf we want to say that someone did something alone or without help, we use the preposition by.
- I am going to Baku by myself.
- Emma lives by herself.
- He painted the wall by himself.
Multiplication and divisionWe use "by" when multiplying or dividing.
- If you multiply five by 25 you get 125.
- 125 divided by 5 is 25.