Recording can be achieved in a number of ways (via the Mixer). While this tutorial only scratches the surface of recording, it should at least get you started. On several occasions I simply picked a poem and read it out loud – then manipulated it and used it for my compositions. Once recorded I can do almost anything with it and mold it into something really cool. No longer was my below average voice any problem. Until I discovered the fun of recording audio and using effects to process it in various ways. So this feature of FL Studio was not relevant for me. I’ve never paid too much attention to this as I neither can sing nor play a ‘real’ instrument. In FL Studio you can record external audio sources that are connected to your soundcard inputs.
FL Studio 9 (and 8) tutorial explaining how to record and manipulate external audio.