The LFO offset sets the level about which the LFO oscillates. The LFO amount controls how far around this value it oscillates.
For example, if the offset is set to 1.0, then the LFO modulates the partial level around its nominal (unmodulated) value.
On the other hand, if the offset is set to 0.0, then the LFO signal itself is being multiplied by the partial, which is effectively ring modulation. This is why the LFOs have such a wide frequency range - because the higher frequencies are useful for ring modulation effects.
The LFO speeds are each controlled by a set of 3 knobs. The centre knob of each set of 3 is the main speed control. By default it has a range of 0.05Hz to 100Hz. Above this is a 'multiplier' knob, which has three settings: '1', '10' and '100'. For example, if the multiplier is set to '100', then the LFO frequency range is actually 5Hz to 10kHz (though the display will still show the 'unmultiplied' value).
The third LFO speed control in each set is a keyboard tracking value. This sets how much the LFO frequency is affected by the note being played. With this control at 'zero', the LFO frequency does not depend on the note. With this control at 'one', the LFO frequency rises or falls by an octave per octave that the note varies from middle 'C' (MIDI note number 60).