How do I make so that you can talk to people?

Like in the Stronghold intermission map, how do I do that?

Eh?

Open the map and look at the script...would be a good start.

http://zdoom.org/wiki/USDF

i would say...take strife...shareware..whatever you got.
and look at it. pull a orange juice box and concentrate.
stare at the script for about an hour. if nothing comes to you. all hope is lost. in fact , imma do that now k?

If you want the NPCs to talk to you maybe try saying hello, asking them how they are or their opinion on something topical

You can't just stand there and expect to make friends.