how??

[Dj Cutter]

how can i record my own voice into FL so that the sound is 100% clean?

[DJ FROGi]

You'll have to use an external program to do the recording, i.e. Adobe Audition or whatever your poison is, and then import that saved .wav file into fruity via a Sampler channel.

[skeggia]

you don't need any external program
just a good mic and keep it at the right distance.
and I suggest using a compressor while recording

[Goodfella]

You can use the Sampler channel, it's OK but the problem is that if you need to work somewhere in the arrangement where the Sampler channel is not activated, you won't hear your voice. Better yet, I recommend using an Audio Clip channel which avoids the problem I just explained.
I belive there's a way to record audio in FL but I really don't know how to do it since I use Adobe Audition for that purpose. And yes, for the 100% clean vocals you need a good microphone, a preamp, and a place that has minimal reflexions so you can later add reverb to your taste.