It's simple really. Just go to the Inventory Forum, and copy and paste the template into a new topic. Be sure to follow the rules and there will be no problems.
As for setting up your inventory button, just copy the link to your inventory topic, go to Profile, go down to where you see **Inventory** and paste it there. Then save it, and look at the bottom of your posts, and your inventory button will appear there.
Simple as that. Enjoy!