First of all, there are two sets of NPCs found in this addon.
The ones under the NPCs category are the runners, they only work in maps with navigation.
The ones under the ENTs category are the teleporting ones, they will work in any map navigation or not.

These NPCs won't work unless the map has a nav mesh.
A nav mesh is what allows the NPCs to know where and where not to go.
Without it, they will simply run forever in their spawn position, being harmless.
To generate a nav mesh, simply goto the console and type;
If successful, the map will reload and the NPCs will start to chase you.

Depending on the map size, the generation will take some time.
Generating a nav mesh with an older / slower computer will result in Garry's Mod crashing.
To fix, type "nav_mark_walkable" in the console while standing on the floor within the map.
Then, type "nav_generate".
Thanks Roach!

Special thanks to KUNOLEO for the video.
https://www.youtube.com/watch?v=ELnA_hworBs&list=UUoXKp_qf5FSBCzC0R2jawxA
Click to Download Navigation Addon for GM_BigCity!

Click to Download Navigation for CS:S Maps!
(Both don't include the maps, just the nav mesh!)

To Enable the Developer Console for commands such as nav_generate, goto the arry's Mod home screen and click options, keyboard and press the advanced button. Then enable the check box for
Enable Developer Console (~)
Now you can go back to your arry's Mod and press ~ under esc in the top left of your keyboard, and the console should show up!
Recap

• Options
  
• Keyboard
  
• Avanced Button
  
• Enable Developer Console
  
• Press ~