Take a look at the example sample material. Ideally, you should have an audio file of 64 measures of a tempo. Each measure should contain a variation of the base pattern. This is easy to do with drum machine software, calling up different patterns and kis on the fly and record the output. Or, an analog sequencer manipulated live is another good example. The index control will move across this audio file.
If you have a short audio file, the index can still be useful, but the indexing itself must be constrained to smaller increments. You’ll notice the offset values: meas and 1/16 above the index preset selector. If you’re using a short audio file, like, two measures, you’ll need to set this to values within two measures (EG 0 measures and 2 1/16ths would index to an eight note offset.