ok, this is pretty easy,
open up your mount and blade unofficial editor.
click on the units tab and add a new troop.
rename this unit whatever you want the NPC to be called.
now, none of these stat boxes are really needed.
Look in the garenteed section and tick the peices of clothing you want your NPC to wear. Dont tick a box if you dont intend your NPC to wear it.
Out of the miscellaneous options you dont want any of the boxes ticked.
under that pick the sex of your NPC.
in the faction box select 'fcn_Commoners'
in the Site box pick the site at which you want you NPC to appear.
The next bit is the important bit, this is the entry number of the scene and directly refers to the entry number variations you get in the object placer/editor thing.
Hire Unit and Hire party boxes can be kept blank.
In the appearance box fiddle with what you want your NPC to look like.
In the inventory add the clothing that you want your NPC to wear. Note: DO NOT ADD WEAPONS, this will make a crash when it tries to load.
Everything else can be left how it is.
Now, go into the scene of which you added them and you should see them standing in the center somewhere doing nothing

Go into edit mode and add the entry point with their variation wherever you want them to stand.
You now have a basic NPC
that guide seems pretty noob proof, tell me if you have trouble.