FLDigi is a great program that, unfortunately, is only really useful for hams and those working on the VoA RadioGram project. There are MANY programs to do digital decoding, and it would appear you've gotten over the big hurdle of getting audio from the SDR to the PC.
I'd suggest starting by reading our article in the wiki on HF digital decoding. Apart from hams, there's a lot that, sadly, is encrypted and we'll never be able to read - but there's still a fair amount of readable stuff if you know where and when to look.
DXing Digital Utilities - The RadioReference Wiki
Notice Chapter 5 - this will give you some easily decoded targets, assuming you have the right software. Look at my sig line for a site that lists just about everything that's out there (I haven't added MARS ALE yet, but I will in the next release...)