The selection of knobs labelled 'Sample' control some basic aspects of sample playback.
The 'Root Note' control lets you set the MIDI note number at which the sample will play back at its original pitch (this is essentially the same as a coarse tune control). A 'Fine Tune' control is also provided.
The 'No Loop On/Off' control lets you disable looping i.e. the sample stops playback once it hits the loop end position. The 'No Loop Fade' control lets you set a short fade-out for this, rather than an abrubt stop. NB the sample will continue to loop during this fade-out, so the settings of the loop controls will have an effect on the sound.
The 'Loop Mode' control chooses between the 3 basic loop modes: Forwards (loop plays from beginning to end), Reverse (loop plays from end to beginning) and Alternate (loop switches between Forward and Reverse whenever it hits a loop endpoint).
'Crossfade Type' selects between 'Equal Gain' and 'Equal Power' crossfade curves. The former is more appropriate when the ends of the loop are similar material, and phase-coherent (for example, if you're looping the sustain section of a sampled instrument). The 'Equal Power' mode is useful when looping less coherent material, and can help to prevent the apparent drop in volume during the crossfade that you can get with the 'Equal Gain' curve.
The remaining loop controls are the 4 coloured sliders that appear in the sample preview window.
'Start Offset' (yellow) sets the point at which playback will start when the note is first triggered.
'Loop Start' (green) sets the beginning of the looped section.
'Loop End' (red) sets the beginning of the looped section.
NB when the Loop Mode is Reverse, Loop End is effectively the loop start and Loop Start is effectively the loop end. Also in this case the Start Offset should be set after Loop Start.
'Crossfade' (blue) sets the amount of crossfade or overlap applied at the beginning and end of the loop. Higher values will tend to smooth the loop transitions.