When you choose the training section on the recording screen, you'll enter Carv's skill development mode.
For each of the major skills (Balance, Edging, Rotary and Pressure) Carv has a skill development that will help you improve your specific metrics.
During a skill development session Carv will be looking for specific metrics to be within a certain range. If they're within the range you hear a good sound (a 'ding') immediately after the turn. If they're outside the range you hear a bad sound (a 'durrh') along with some feedback on how to improve.
There are 20 levels for each skill. As you progress up the levels, the range gets smaller and smaller and it becomes harder and harder to pass. Some people find level 5 difficult to pass, others level 15. Good luck!