you slice the sample into something that can be looped nicely, then you can assign it straight to a pad and have a loop for your sequence (if it's properly tempoed).
you can send the sample out across the pads with patched phrase. some instruments call programs patches. it takes the PHRASE and a PROGRAM inside the MPC; then you can open that program in a track and sequence the slices however you choose.
the pitch and time stretch work some math magic to allow you to play the sample back at a different tempo without changing the pitch, or vice versa.
there are numerous tutorials on YouTube, do a search....
