Each button or slider has rollover tooltip help to tell you what it is, as well as listing the associated key command in parentheses. For example, the first sine wave button on rollover will report: sine wave OSC (q).
Spongefork is built off the idea of frequency modulated oscillators. With this in mind, OSC refers to the carrier wave and MOD refers to the modulating wave. Dragging in the XY window will change the frequency of both oscillators at the same time. The X axis is mapped to the OSC and the MOD is mapped to the Y. In order to hear the modulation you will need to have the modulation depth slider set above 0.
Frequency range refers to the upper pitch limit. This slider changes its function based on what mode you are playing in. The basic modes are either free pitch, locked to pitch, or play keys.
The playlist is for managing and playing your samples. Samples can be loaded into the OSC and MOD by double or option double clicking the file name or pressing CMD 1 or 2. Files are started, stopped, or looped using the associated button on the right side of the playlist. Files are removed by pressing delete. All of these commands can be done on multiple contiguous selections.
NOTE: Capture to disk, storing presets, and saving playlists are disabled until you unlock Spongefork with a valid registration code.
Input record will capture from your selected sound input device into memory. Once you have recorded some audio, you can use the buttons to load it into the OSC / MOD or save it to file / add it to the play list.