You can create an FTP user in Addemar by going to 'My Account' -> 'Users'.

Click on the 'New FTP user' buton. When you Click it, you will see the address + username and you will have to enter a password which you will use to login the FTP using the FTP software.

FileZilla is an example of an FTP program. It's free and easy to use and can be downloaded here:  http://sourceforge.net/project/showfiles.php?group_id=21558&package_id=15149&release_id=607101

Below: a screenshot of FileZilla as an example:
 

On the upper side of the program, notice the 3 fields you have to fill in with the data you received after you created the user (Address, user and password).
When you enter these credentials, you can click on the "Quick Connect" button.
Two panes (left + right) will appear. The left one is your local disk, the right one is the disk from your Addemar account. You can then drag files or folders from right to left to download them, or left to right to upload them.