Hi,

The json file link is for information.

When you click the name of a hardware it becomes dimmer which means it has been added to your .json config list.

Then click rescan (sometimes twice) and the list below of available hardware to install will have a new entry or entries allowing you to download or remove the hardware.

The list of discovered hardware is simply the list from the arduino third party hardware page but you can find other .json files on the internet. The discovered hardware simply avoids you adding the json manually.

If you read the documentation for the arduino ide boards manager you will see you have to enter the .json files into the preferences dialog. This is the "published" known way to install hardware, visual micro just makes it a bit easier.

You can see that in the arduino ide file>preferences and the board manager is at the top of the board list in the arduino ide. I would recommend you install via the arduino ide so you understand the board manager system then visual micro will make more sense (it's the same system)

In fact if you install via arduino then the hardware is available to both ide's, if you install via visual micro then arduino won't see the new hardware

On visualmicro.com you can always find the documentation index which also describes some of the board manager
Board Manager Documentation

Any jsons added by clicking the auto discovered list can be seen in the list on the visual micro ide locations configuration window where they can be entered manually.