Hello,

Your problem is resolved. You do not see anything in the cart and checkout page because you did not have the element for cart functionality and for the checkout functionality in your pages. But now I add the cart element and checkout element and your cart,checkout is working just fine.

Screenshot for clarification: https://jmp.sh/ROM2Qco

If you want to edit the sidebar you need to go to Appearance >> Widgets >> Main widget area.
Screenshot for satisfaction: https://jmp.sh/sLM3uj2

Best Regards.