You need to read the Trade Corner rules found here to familiarise yourself with how the section works before you post a shop. That thread's got some links and advice for making a shop work well inside it, so make sure you take a really good look.
As for permission - you don't need permission, per se, but when you post your thread it'll have to be approved by a moderator before it shows up to everyone else. So don't worry when your thread disappears for a while after you submit it; this is normal.
If you need help beyond what the rules and existing threads can provide, you can send a PM to either Mac or twistedpuppy, although I believe the latter is having Internet issues. Have fun!
edit: wow ok ninja'd. Oh well.