Installation is split into two steps, the server installation, which means installing sourcemod.js and SourceMod onto your Source server, and the client installation, which means installing the npm module and connecting.
Make sure you have the following before continuing:
- Node.JS
- NPM (should come with Node)
- Any Source server (Team Fortress 2, Counter-Strike: Global Offensive, etc)
- An internet connection
Once you've gotten the prerequisites, go ahead and start off with the server installation.