1) If you can get the data from the bank as .qbo (web connect) that would be ideal…. as you don’t have to convert anything or finagle with a spreadsheet. And bring everything via Bank Feeds / Downloaded Transactions in QuickBooks Online
2) If no .QBO file available, then the next best choice is a CSV file… you can open that in Excel and do some interesting cleanup work with will help immensely during the import process. QuickBooks Online will let you import a CSV file, but restricted to 3 columns: Date, Payee, Amount (missing NUM and MEMO; which is a BIG issue!) But, you can use CSV2QBO (a $60 software) to make the excel/CSV File import into Bank Feeds / Downloaded Transactions in QuickBooks Online as a QBO/Webconnect File with all the fields.
OR, if only have a PDF bank statement, then you need PDF2QBO ($200 software) to convert the data to .QBO/Webconnect and use Bank FeedsDownloaded Transactions in QuickBooks Online with all the fields
These are NOT easy concepts, you may need to watch this 1 hour video to understand the mechanics:
If you want private one-on-one training on how to do this, you can hire Hector for $500, the training will last about 90 minutes, and he can help you do you first import with you.