I did a "go get" to install github.com/chsc/gogl. Apparently this seems to have put stuff in C:\Go\src\pkg\github.com\chsc\gogl. And when I import "github.com/chsc/gogl" I can use the package just fine.
But suppose I wanted to make some edits to the package. How do I manage and organize my projects and code? Where do I put my copy of gogl and how do I get all my projects to use my copy of gogl instead of the one installed under C:\Go\src\pkg\github.com\chsc\gogl?
You could modify the code in C:\Go\src\pkg\github.com\chsc\gogl, and run "go install github.com/chsc/gogl".
Alternatively, if you are going to be making changes for the long term, your better bet is to fork that project on github, and use your fork instead (github.com/yourname/gogl).
You can have a copy of gogl from github.com in your project folder:
make the C:/my_go_project/local_github.com/chsc/gogl folder
copy all the contents from C:\Go\src\pkg\github.com\chsc\gogl to C:\my_go_project\local_github.com\chsc\gogl
include your library in your .go files like
import "local_github.com/chsc/gogl"
Now you can edit your local copy as you wish.