by, buy

Buy means to purchase or obtain with money--
I am going out to buy some pastry.
Let's go out and buy a pizza.

By or by is used to denote the maker or author of something--
This pastry was made by the baker.
By or by is also used to describe how something moves or works--
The baker's oven is powered by gas.
I got to the bakery by train.
By or by can also mean during the time of--
The baker works by night.


Now that you know that, you can say--
"I want to buy some pastry made by the baker downtown."

Note--"bye"  means an odd or extra something--
The bottom of the ninth may be a bye.
Note # 2--"by the bye" means by the way or incidentally--
By the bye, we won't have to work late tomorrow.
Note # 3--"by and by" means at some time in the future--
"In the sweet by and by we shall meet on that beautiful shore..."
Note # 4--"by-by" or "bye-bye" means so long or farewell--
Watch the baby wave by-by.