How do I download this mod there is nothing in the text that says how to download it.

You download and install SecurityCraft like any other Minecraft Forge mod. I'll give you the links to a few videos below in case you don't already have Forge installed.

SecurityCraft's CurseForge page (where you will download the mod from): https://www.curseforge.com/minecraft/mc-mods/security-craft
How to install Forge on 1.16.2: https://www.youtube.com/watch?v=rgy1HiR-W9I
How to install mods on 1.16.2 (the video even specifically shows SecurityCraft being installed): https://www.youtube.com/watch?v=WqSC5glbPCw