You'll find the ability to export/download your transactions into a .csv file (spreadsheet) in the top right of the main Transactions screen. Click on the downward pointing arrow icon next to Results Summary to export a .csv file.
The download will include all transactions in the current view, i.e. any filters applied will be taken into account, and will include date, account, original description (as it appears at the bank), custom description (if you have amended it), value, and the tag applied.
Please note that this function is not available when using Safari, and is also not available on the mobile apps.