Hi @Buttercup
The best place to start is in the knowledge base and the search feature on the forums. This covers a lot of the questions you’re likely to have.
Tagging a transaction simply associates a bank transaction to an invoice, a transfer, a payment to a supplier, and so on. They’re quite flexible but it helps with things like the VAT calculations. We have a useful guide on this, here: Tagging your bank transactions
It’s good practice to create a new client or supplier record to help with filtering invoices (e.g. you can see exactly who owes what, or what you owe and where), but it’s not always practical to do this, if for example you’re selling on Amazon, eBay or similar. In this case, you can create a generic client and call it “Amazon Sales”, or “Website Sales” - what ever is appropriate. This post may help: VAT for amazon seller Do I have to create an invoice for each sale? - #2 by rhc
The key thing is, if HMRC ever ask you to prove a transaction took place, could you? With things like the bulk sales, you would usually attach a report from the relevant place. So, you could attach a daily sales report for example.
Hope this helps!