Select the guide for the required operating system:

• Windows
• Linux

Windows

Let's go to releases and download the library we need as shown in the screenshot

After downloading, open Steam, find Garry's mod in the library of games. Right click on Garry's mod -> Properties -> Local Files -> Browse local files. The explorer will open with the game folder. Go to the garrysmod/lua/bin directory. Copy gmsv_mongodb_win32.dll to the directory.

And the library is installed!

Linux

Open the console and go to the directory with the server. After that, go to the directory with libraries:

$ cd garrysmod/lua/
$ mkdir -p bin # Create folder if it doesn't exist.
$ cd bin

# Downloading the library
$ wget https://github.com/Pika-Software/gmsv_mongodb/releases/download/2.1.0/gmsv_mongodb_linux.dll

And the library is installed!