Download the latest binaries from here and extract them somewhere in your Unity project's Assets folder.
Download the repository and extract it somewhere.
Then from the extracted folder copy the Archon.SwissArmyLib folder into your project Assets folder somewhere.
Do the same thing with the Archon.SwissArmyLib.Editor folder but place that one in another folder called "Editor".
That's it! You can freely start using the library. Check out the sidebar for some help with using the different utilities.
Just download the project, open the project in Visual Studio (or use MSBuild via CLI) and build it. There's nothing more to it.