The preposition by is used in many different ways.
One common use is in place phrases. In showing
places, the meaning of by is the same as beside or
at the side of.

Examples:

Were you sitting by (beside) the door?

Joe parked his car by (beside) mine.

The police station is by the court house, isn't it?

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When by is used with a verb showing motion,
it usually shows movement past a place:

We walked by your house this morning.

Who was that man who just ran by us?

We drove by many motels before we found one
that had a "vacancy" sign.

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With a personal pronoun (me, him, her), by also
means "in an easy-to-reach place" or "handy":

Hilda always has a calculator by her when she
balances her checkbook.

Norio keeps a map by him when he drives to
a new place.

Do you have a dictionary by you when you write
essays in English?

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When by is used for time, however, the meaning
is not later than:

The meeting will start at 9:00. Please be here
by (not later than) 8:55.

My flight leaves at 1:30, so I need to be at
the airport by (not later than) noon.

I expect to finish my report by (not later
than) Friday.

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Special Note:

When by is used with a "normal" personal pronoun,
it means "in an easy-to-reach place" or "handy," but
when by is used with a reflexive ("self") pronoun,
the meaning is alone or without help:

Did Simone fix her car by herself? (Did she
fix her car without any help?)

No, thank you. I can do this by myself. (No,
thank you. I can do this alone. I don't need help.)

Youssuf is paying his college costs by himself.
(Youssuf isn't receiving a scholarship or other
financial help to pay his college costs.)

Hyo-Jin and her husband didn't paint their house
by themselves. They hired someone to help them.