In the top-left corner you can see your ETH balance. In the top-right corner you can see your PEARL$ balance.
1) Add items to the cart by clicking on the plus, you can add multiple items of multiple categories.
2) As soon as you are ready to buy you can hit the "approve" button, which will bring you to your metamask.
3) Make sure to wait for the transaction to go through before you go to the next step.
4) After the approval you can hit the "Buy All" button to buy your items.