Go – $GOPATH must not be set to $GOROOT, why not

GOPATH is discussed in the cmd/go documentation:

The GOPATH environment variable lists places to look for Go code. On Unix, the value is a colon-separated string. On Windows, the value is a semicolon-separated string. On Plan 9, the value is a list.

GOPATH must be set to get, build and install packages outside the standard Go tree.

GOROOT is discussed in the installation instructions:

The Go binary distributions assume they will be installed in /usr/local/go (or c:\Go under Windows), but it is possible to install the Go tools to a different location. In this case you must set the GOROOT environment variable to point to the directory in which it was installed.

For example, if you installed Go to your home directory you should add the following commands to $HOME/.profile:

export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin

Note: GOROOT must be set only when installing to a custom location.

(updated version of Chris Bunch's answer.)

• GOROOT must reference the folder where you installed GO
• GOPATH must reference an empty folder which will be your workspace (src/pkg/bin for your projects)

Add those two variables in your user environment variables.

A go get github.com/coreos/etcd should:

• download the sources in %GOPATH%/src/github.com/coreos/etcd (src is created for you)
• compile it in %GOPATH%/pkg/windows_amd64 (pkg/ is created for you, windows_amd64 reflects your windows architecture)
• with go install, install it in %GOPATH%/bin (bin/ is also created for you)

Note: with Go 1.8+ (Q2 2017), GOPATH might be set for you by default to (on Windows) %USERPROFILE%/go.
On Linux, it would be $HOME/go: see issue 17262.

Update 2018, three years later: GOPATH is becoming obsolete with Go 1.11 modules:

mkdir newProject
cd newProject
set GO111MODULE=on
go mod init myproject