Publicado originalmente por pillow:

Introduction

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.

To get them running

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;

nav_generate - To Create a Navigation Path nav_save - To Save the Created Navigation Path

If successful, the map will reload and the NPCs will start to chase you.
If "nav_generate" prints an error to the console and doesn't work, stand on a surface where you want the NPCs to be compatible, type "nav_mark_walkable" (without quotes - you can do this multiple times for different surfaces before the next step), and then type nav_generate. If the map restarts, the NPCs shouold now be functional.

Problems

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.

No valid walkable seed positions. Cannot generate Navigation Mesh. Unknown command: bot_kick

To fix, type "nav_mark_walkable" in the console while standing on the floor within the map.
Then, type "nav_generate".
Thanks Roach!

Video Tutorial

Special thanks to KUNOLEO for the video.
https://www.youtube.com/watch?v=ELnA_hworBs&list=UUoXKp_qf5FSBCzC0R2jawxA

GM_Bigcity Navigation

Click to Download Navigation Addon for GM_BigCity!

CS:S Navigation

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 :gmod: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 :gmod: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 ~