Making A Plug In For Inventory

I have been trying for a week or so to find a nice tutorial on making wordpress plug-ins. I really need some advice on how to go about creating a plug in where I can add inventory to my site. What I would need to have with this plugin is picture, place to describe the product, price. I know there are plug-ins somewhat similar to this already, I just want to create one for myself because I need to add additional things. Any help would be greatly appreciated.

Thanks,

Sean