Hi Steve46
Welcome to the UK Community Page for QuickBooks Online.
You can add the transactions through the Plus Icon - Invoices for Sales, and Sales Receipts for Sales which are already paid, or where there is no invoice. Expenses and Bills are the purchase options, Expenses are already Paid, Bills can be added that are yet to be paid.
When creating the transactions, you can change the date to the correct date for that historical transaction and save,
We do have an option also, where if you have this information on your bank statements (if all paid transactions), you can historically import the statements in a .csv format into the banking section, and add them from there. This may be easier, but it depends on the detail and outcome you want on the transactions.
Let me know if this helps, or if you'd like me to elaborate on anything.
