This is pretty basic.
You load up a sample, and assign it to a key, or a range of keys. Lets say you load a break and want to play it from C4. From the left hand side, select the sample, and find the part about "zone range". This means the zone of the keyboard this sample will be played from. Drag them all (low key, root key, high key) to C4 - Or alternatively click the black 'multi' tab and drag the grey vertical column sideways to C4.
Now when you use C4 in the piano roll, the sample will play from the sampler.
If you are using a break, I suggest you slice it: Just below the sample image there is a dropdown menu that has all the possible playback options in it - select 'Sliced (keymap)'.
Then by right-clicking the sample select 'split slice' and a new slice will appear. These will play then from c4 and c#4 respectively.
However, for break works I suggest sticking to the fruity built-in slicer, which will get you there a lot faster. The only drawback is that it doesn't allow for different slices to be output to different FX channels. In Shortcircuit this is achieved by first slicing the samples, then right-clicking on the slice and selecting Slice -> zone. Then you can select the new zone and output it to a different bus. If you have multiple outputs enabled in fruity, they'll go to different FX channels.