Well im not all that good with this but ok
1. make an event
2. go into event double click in the list of events commands
3. scroll through to page 3 and look for ( shop Processing)
4. click on that and you will find yourself with an empty box click in that and another box will pop up and it will have 3 tickable features item,armor and weapon find the item you want in that and click ok or wat eve.
and thats it put as many items etc as you want..
To edit prices go into data and find the item of your choice and change it within there