Essentially two options:
1) Obtain a burning program that decodes FLAC files. I use Ashampoo Burning Studio, which is payware (about 30 bucks). It's a nice program and fully supports FLAC. Foobar 2000 (freeware) also supports FLAC, although I think you need to find an add-in to burn via FB. Do a little Googling, FLAC is becoming pretty widespread.
2) Decode the files yourself for burning with non-FLAC-supporting burning programs (like Windows Media Player or others). The FLAC front-end program lets you convert FLAC files back to WAV, with the option to keep the FLAC source file or delete it after conversion. You can always convert a WAV back to FLAC and vice-versa. That's one of the primary advantages of it.
Hope that helps!