Start CSV2OFX, it will show the file dialog to locate a one or more of CSV files. Click on the file (or hold CTRL and click on more than one file to select multiple files) and click Open on the file dialog.
Review the Transactions tab. If you notice that certain columns should reassigned, click the Review Mapping button and assign columns from your original file to the columns on the sidebar (for the Mac version, simply assign columns on the sidebar).
Return to the Transactions tab.
Click the Save button to save loaded transactions to OFX file.