Start WSL, say by opening a terminal window in it. Then in an Explorer window navigate to:

  \\wsl$

Or, in the terminal cd to your homedir and then type "explorer.exe ." including the dot. This will get you specifically to your homedir.

Where to set global environment variables (and I mean global for all users here!) depends on the distro. On Debian and most derivatives, you can use /etc/environment for this.

The ~/.bashrc file usually.