1) Connect on your database, then the table player,
2) Open the table Shop and Shop_item
In Shop you have to define which Npc have which Shopvnum, if you look at it, you will understand it.
In Shop_item you have to choose, which Npc sell which item.
In Shop:
Vnum => You can choose the Vnum from the Shop. That Vnum you will need in Shop_item, to define which Npc sell the item.
Name: Name from Npc, its just for you that you can look, if you would like you can type "adsadska" or something like this.
Npc_vnum: Vnum from the npc, you find it at the mob_proto
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In Shop_item:
Shop_vnum: There you have to put in the Vnum, which you choose in Shop!
Item_vnum: There you have to choose, which Item the Npc have to sell.
Count: The Count of the Items
Sorry for bad english :P