Some common problems when using the tools.
The menu in the top right of the Explorer should have four buttons: "Plugins", "Preview", "Mod Manager", and "About". However, on first downloading and opening the tools, you may not see "Plugins" (see image below).
To solve the problem, you'll need to unblock the .dll files included with the Explorer. Right click on each file, choose "Properties", and select "Unblock".
When you launch the Explorer again, "Plugins" will now be available.