You can add a new NPC with pokered easily by just adding a new object (person) and incrementing the person counter. For example:
object SPRITE_OAK, $5, $2, STAY, DOWN, $5 ; person
SPRITE_OAK is the NPC's sprite.
$5, $2 are x and y coordinates respectively, from the top left corner of the map. The $ symbol is to denote that the number is in hexadecimal, just like % denotes a binary number. So for example $a is the same as 10, and $5 is the same as 5.
STAY, DOWN means that the object is static and that it is looking down by default. Use WALK, $0 if you want the person to move around (also WALK, $1 for only vertical movements and WALK $2 for only horizontal movements), and use STAY, NONE if you want the person to rotate its facing or if it's only an object with a single facing defined (e.g. ball or dex sprites).
The last $5 is the text/script id. In general it should be the same as the object number for simplicity, unless you want to use the same script for multiple objects.
To remove a warp you have to remove both its entry in "warps" and in "warp to". If you remove a warp only from one place you will shift the other warps so they will no longer warp to where they should.
Let's see how warps work. This is the first warp in Pallet Town:
; warps
db $5, $5, $0, REDS_HOUSE_1F
(...)
; warp-to
EVENT_DISP PALLET_TOWN_WIDTH, $5, $5 ; REDS_HOUSE_1F
(...)
REDS_HOUSE_1F is the connected map.
$5, $5 are the x,y coordinates where the warp is at. Note that unless the warp is in a tile whose collision allows warping (e.g. a door), it won't work.
$0 is the "warped to" id within the destination map. Red's House 1F has two warps, one to Pallet Town and one to your room. $0 refers to the first warp (Pallet) and $1 would refer to the second (your room). If you checked out the Red's House 1F file you'll see how its first warp entry warps to Pallet Town so that the two connected warps match.
PALLET_TOWN_WIDTH is the connected map's width, and $5, $5 are the x,y coordinates again.
A warp could also look like this:
; warps
db $b, $4, $2, $ff
(...)
; warp-to
EVENT_DISP OAKS_LAB_WIDTH, $b, $4
(...)
In this case we have $ff instead of the connected map id. $ff will be interpreted as the last map we were at. You can use this when it's certain that coming back to the previous map is the only possibility. For example if you go through a warp in Oak's lab the only option is that you're warping to Pallet Town, which is the map you'll be always coming from. But if you're at your house, you could be coming from your room upstairs and then exit through the door, so you can't use $ff here.