The most common task when using Quickbooks is to enter transactions. Often banks provide transactions through online banking. Instead of entering transactions by hand from the printed paper statement, check first which format your online banking provides.
QuickBooks 2020-2023 imports QBO (Web Connect) files as the easiest option to import transactions. Quickbooks provides the Bank Feeds interface to "match" transactions to vendor records after import and assign expense/income accounts and add transactions into the register.
Quickbooks Desktop imports the IIF format, which allows specifying vendor name and expense/income account (category) and import transactions directly into the register.
You have to be precise with vendor names and expense/income account names, so it is a good idea to get your transactions into CSV/Excel format first, edit them and then convert them to the IIF format
Use the ProperConvert app to convert transactions to CSV format
After CSV/Excel file is edited, use the ProperConvert app to convert to IIF
For older Quickbooks, IIF format is the only option to import. Use the instructions above to get your data into IIF format
If your QIF file has categories as your expense/income transactions in Quickbooks, use ProperConvert for quick conversion from QIF to IIF.