You’ll need a column for the field name you want to import. In that column you’ll put the field values.
The column name doesn’t have to match the custom field name, but if it does the plugin will default it a mapping for you. If not, you can enter a mapping from the input column to the WordPress custom field in the TurboCSV import screen.
Please see the TurboCSV documentation for some more info.
There’s also a file called ‘sample2.csv’ (and sample2.xlsx in Excel format) in the plugin directory. It has an example of a custom field column so it may be useful to take a look or try importing it.