@dyedgrey $GOROOT is where the toolchain is installed. $GOPATH is effectively where your user cache is, typically ~/go. Generally, these should be unset and let the defaults happen. You can run `go env` to see what it knows. You should add $GOROOT/bin to your $PATH and could add $GOPATH/bin as well.
As for go.mod, this is the "new" way of developing go apps. Used to be you needed to put them under $GOPATH but you actually shouldn't do that now. I put everything under ~/src myself.
@dyedgrey See https://go.dev/blog/using-go-modules for more information.
Effectively, go.mod is a dependency manifest similar some other package managers' "dependencies" section e.g., npm (Node.js) or cargo (Rust). Develop these outside $GOPATH like you would with any other language. For ease of working with a group of disparate modules, read about go workspaces: https://go.dev/blog/get-familiar-with-workspaces
