Lego dimensions ps4 buy red stones?

I have been playing Lego Dimensions for some time and have already collected some red stones. You can see this if you go to start and then on extras. But how can I buy the stones, because with the collected stones is only available for purchase "…

Would be grateful for answers

If you're on the portal in Hub World, you can go to the portal, where you can also choose levels and worlds. Then you can buy them, if you click on the red stone, which is shown.