The csv format is essentially a table of rows and columns. It is very versatile and it is not specifically designed to contain financial information. As such there is no standard way a bank would use to store data in such a file. Which is to say there is no standard order for the columns in a csv file or names for those columns. As a result of this the import process for csv files is much more involved that any other standard format. The text file importer allows you to specify which columns in a csv file should correspond to which fields in a Moneydance transaction.
Once you have installed the "Text File Importer" extension a new menu item will be available on the extension menu called "Extensions->Text File Importer". Select "Extensions->Text File Importer" and you will be presented with a window asking you to browse to the csv file you want to import. Click the browse button and browse to the csv file then click Next.
The next window allows you to specify the account you want to import the data into. You can also specify if the fields in the file a separated by a tab or a comma. You may also need to change the date format to that used in the file. Click Next.
You will then be presented with a windows that has a list of fields. Each of these fields represents a column in the csv file. e.g. "Field 1" is the first column in the file and "Field 2" is column 2. You need to select which Moneydance transaction field should correspond with which field in the csv file. You will need to open your csv file in a text editor and take a look at it to determine which column is which.