As you are from the UK, you wouldn't need any of the tax documents from that tab. Only stores which would need them would have this tab show up. You wouldn't need pay VAT on your fees with Shopify since Shopify doesn't charge VAT in the UK.
To access your invoices you can do this by taking the following steps in your admin: Admin > Settings > Billing > Bills.
Shopify has a guide going through everything you need to know about your bill also which you can see here.
Hope this helps!
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