Quando utilizar o "BY"

I have some problems my friends!
Never know when I use "by"...someone may explain it for me?
For example:

"People rushing by"
"Times goes by"

I just can use it when is before "someone" or "something"...
like:

by him, by the dog...

I expect that you have understand my doubt!

I'm trying writing in English! uahuahuhauhau \o