Well for sampling in FL Studio, you could use one of the Audio editor programs called Edison. Like for example load a sample or song under the sampler and you should see a tab for the specific sample and at the bottom of the tab right click and click edit. That should take you to Edison.

The trick in making the sample work in FL Studio is to find the correct tempo obviously. Also I use 16 bars on most tracks.

Personally though I use Cool Edit Pro 2 which is now Adobe Audition. CEP is everything I need for creating samples and chops. But Edison is just as great.