Hey there @Donomah, looks like you have the "Store" option selected. If you look slightly above your inventory, there are six options there -- Place Item/Open Capsule, Sellback, Store, Add to Market, Add to Usershop, and Create Personal Trade. If you'd like to place items, select Place Item/Open Capsule and then you'll be able to do so.

Thanks for posting a screenshot too, that helped greatly in determining the problem!

Please let me know if you have further questions! ^^