It's a fairly complicated process really... but, here's my take:
You need to get a bunch of cash saved up for your initial investment. In this initial investment, you will need to rent out a building, or a piece of land (and build a place). You then need to contact a bunch of major companies and make 'reseller' partnerships so that you are allowed to sell their stuff in your shop.
Umm, yeah, that's it. But starting a business like that is pretty damn complicated.. you have to pay staff, buy equipment (cash register, racks, signs) you have to market it, etc...
You have to register your shop with the government, buy insurance, get tax licenses, etc. etc. etc.
I guess that's about as simple an explination you can get.. ?
Matt