These instructions will provide you with the steps to install the Monogame program templates, and the Monogame Content Builder tool.
Monogame is an extension that can be added to Visual Studio using the Extension Manager. Here are instructions:
https://docs.monogame.net/articles/getting_started/2_choosing_your_ide_visual_studio.html
Note: Once you have chosen to add the extension in the extension manager, you will have to close Visual Studio in order for the installation to happen.