How to comply with my requests?

I want to make a request but I am not a very good scripter for linking certain things or how to address them specifically to get what I need or want. I want to figure out how to make it so there is a enemy NPC able to find people only whats infront of him/her rather than range like in most NPCs, I also want to know how to make a NPC walk specifically from places like if they're patrolling, and I want it to activate a script once the NPC finds the player. TBH, I would just think it'd be a invisible part with a Touched script on it welded in front of the NPC would work but I don't know.

Also, the NPC is basically a guard and the player is a trespasser/criminal

This website doesn't take kindly to requesting so I don't know but hey at least they could take a question. :)