Okay this might be wrong since I'm pretty noob too buttt
I think you just click the change avatar button on that left bar to get to your person. Click on wadrobe when you are in there to get to your clothes. Your items in your inventory should be in your wadrobe already I think, just go through the menus on the bottom where it says accessories/addons etc.
And to change your forum avatar click on the preferences button on the left bar and then hit forum options.
Normal User