FDM is NOT designed for downloading from Usenet binary newsgroups. Use some binary newsreader instead.
FDM uses automatic network management for determining available bandwidth. It takes about 1 minute for FDM to determine your connection speed so running download for the first time you should just wait. The bigger download the more accurate FDM is. If you don't like it, go to FDM menu Options | Settings | Downloads | Network, select "Choose..." for connection speed and set all available parameters manually. Then you can go to Download | New downloads option, click "Advanced" button, choose "Connection" tab and set other connection parameters.
You can also read other topics about this FDM feature, use "automatic network" or "automatic speed" as keywords.
Andrzej P. Wozniak, FDM user and forum moderator
Read "How to report a bug or a problem with FDM"