Umm... did you try reading the manual?
Here's a link to it as a PDF File.
Did you talk to the vendor you bought the SSB from???
Did you do the installation yourself? If so, did you setup the antenna and ground plane properly??
Saying that you can't figure out how to use it is kind of vague...what exactly is the problem you're having?
Is it that you can't turn the set on?
Is it that you can't find anyone to listen to on it?
Is it that you're not getting any reception on it?
Really vague statements like "I can't figure out how to use it." are generally going to get relatively sarcastic and unhelpful responses. It would help a lot if you would narrow the scope of the problem a bit.
Do you know the installation is done properly and that the SSB set is working? If not...then that would probably be the first step, especially if you did the installation yourself and don't have a good foundation in marine communications or electronics.
If you can confirm that the set is properly installed and operating... then you need to find someone to talk to or listen to. Be aware that the quality of the signal will be affected by what time of day, the sunspot activity, your proxmity to large RF interference sources—like military bases and airports, and what exact frequency you're using.
Also, a more complete list of the equipment you have would probably help. Do you have an automatic tuner, or is there one built into the Furuno? If not, do you have a manual tuner, or are you using different antennas for the different frequencies—and yes, I know of at least one guy who does this, but he's a dinosaur and a bit eccentric.