Okay I will try to make this much simpler than he has.
Step 1:
open your gfx file (the one you want to edit)
gfx001 = GUI 1
gfx002 = GUI 2
gfx003 - gfx007 = Map gfx
gfx008 = Race/Skin
gfx009 = Male Hair gfx010 = Female Hair
gfx011 - gfx012 = Male/Female Boots
gfx013 = Male Clothes gfx014 = Female Clothes
gfx015 - gfx016 = Male/Female Hats
gfx017 - gfx018 = Male/Female Weapons
gfx019 - gfx020 = Male/Female Wings/Shields/Arrows
gfx021 = NPC
gfx022 = Map Shadows
gfx023 = Icon/Accessories
gfx024= Spells
gfx025 = Spell Icons
Step 2:
Click Action tab.
In drop down list click "Add a New Resource" (you will need to do a bit of math before hand to see how the numbers increase from item to item in each gfx file)
Select your 1st 24-bitmap image to add.
Under "Resource Name:" add the next number in the numbering sequence that you figured out above.
Repeat for however many more 24-bitmap images there are for the item/npc/ect.
Step 3:
Save
Step 4:
Now go to the item before the one you have just now edited, figure out what its called.
Open Pubedit or Editpub and the corresponding file (eif,esf,enf)
Locate the item to find its "GFX #" your new item will be that number +1.
Step 5:
To get Icon #, Open gfx023 add the ground view first then the inventory view second the same way you did in for example gfx013.
Save
Just like before look at the item before it and find that in the pub file. This time look at the "Icon #", your new item will have that icon number +1