1. By indicates an actor, instrument, or cause

Pattern: be + past participle + by + noun
The work was done by a carpenter.
The mark was made by a hammer.
The damage was caused by the storm.

2. By means following the boundary of something; along
They walked by the side of the road.                                                   

3. By indicates a method or way.               

Pattern: verb + (noun) + by + noun
She made a little money by begging.
We sent the letter by air mail.
They went to the mountains by Route 66.        

4. By can mean according to a form, period of time, packaging, weight, number, or amount                                                    

Pattern: verb + (noun) + by + the + noun
He makes his decisions by the rules.
She charges by the hour.
We buy eggs by the dozen.                                         

Typical nouns after by the:
day, hour, month, week
job, piece
bag, barrel, box, bucket, bushel, cup, drop, gallon, ounce, pint, pound, quart, ream, tablespoonful, teaspoonful        

5. By can mean not later than.
You must be here by six A.M. sharp.
I'm worried; they should have arrived by now.            

Expression:
by the time—when
By the time you get up, I'll be in New York.                 

6. By means near or next to.
His desk is by mine.
I hope you will stay by me.                 

7. By indicates multiplication, division, and square measurement.
We multiplied four by three. (4 × 3 = 12)
They divided ten by two. (10 ÷ 2 = 5)
That room measures ten feet by twelve feet. It measures 120 square feet.                    

8. By can mean a lot of.   

Pattern: by + the + noun
He gets letters by the hundreds every day.      

Typical nouns used after by the:
dozens, hundreds, thousands, truckload        

9. By can indicate the extent of a win or a loss.
That horse won by a nose.
They lost the basketball game by three points.            

Expressions:               

by a mile—by a lot; to a great extent
We won the game by a mile.                           

by far—without question
He is by far the strongest man here.                

10. Expressions                   

by all means—certainly
You should by all means visit the art gallery.              

(all) by oneself—alone; without help
The children are at home by themselves.
The girl made the cake all by herself.              

by day—during the day; by night—during the night
Most people work by day and sleep by night.                         

by chance—for no apparent reason
I saw my teacher at the mall by chance.          

by (any) chance—perhaps
Do you by any chance have change for a dollar?        

by the way—incidentally
By the way, my aunt is coming to visit next week. Why don't you come see her?                   

little by little (adverb)—slowly
He practiced every day, and little by little, began to show improvement.         

one by one—one at a time; two by two—two at a time
One by one, she picked up the pearls from her broken necklace.
The schoolchildren walked to the museum, two by two, holding hands.         

by profession—indicates one's job
He is a teacher by profession.             

by nature/by disposition—naturally
She is generous by nature.
He is nervous by disposition.                          

by reputation—indicates common belief
She is a good lawyer by reputation.                 

go by the board—be ignored
Our suggestions for improving the company went by the board.        

by and by (adverb)—one day, in the future
We'll meet again, by and by.                          

by and large (adverb)—almost completely
The company is doing well, by and large.          

11. Phrasal verbs              

do well by (nonseparable)—be responsible for someone's benefit
She was a good mother; she did well by her children.                        

stand by (nonseparable)—to support
She stood by me when I was in trouble.          

swear by (nonseparable)—have complete faith in the worth of something
My mother swears by that cleaning product.                                                               

drop by (intransitive)—visit without notice
Your friends dropped by this afternoon, but you weren't here.            

drop by (separable)—to deliver
A boy dropped this package by today.            

get by (intransitive)—live, but with difficulty
He's feeble, but he gets by.                                         

go by (nonseparable)—pass in front of
We went by your house last night.                  

put by (separable)—store
She put her dreams by for a while.      

run by (separable)—to tell in detail
She ran her story by me several times this afternoon.  

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