Installing Client-Side Mods
This tutorial is done in Linux, but can be applied to Windows.A more detailed tutorial can be found on the Minetest Wiki.
1) Navigate to the Client-Side Modding section (you should already be here), and find a mod you wish to install.
2) Navigate to your minetest directory (.minetest on Linux) and create a folder called clientmods if it does not exist.

3) Download or clone the mod.
5) Open mods.conf in your favorite text editor and add load_mod_modname = true (where modname is the name of the client mod you downloaded). Save the file.

6) Open Minetest and navigate to the Settings tab. Select Advanced Settings. Navigate to Client > Network > Enable Client Modding or search for "client". With Enable Client Modding selected, select the Edit button and change the displayed option to Enabled in the dropdown, or simply double-click the setting. Save your changes.

Your client-side mod has been enabled!
Type .help all in chat to see what you can do!