How can you skid / How to do skids / skidding

Spin to win... It will improve your cadence and fitness. Otherwise why not just ride a geared bike if it's 20 straight country miles?

I just find it's more fun fixed, easier to chuck it about, easier to maintain speed (for me), feels like it's doing more good in terrms of fitness. Cadence is giong up over the months etc..

Thanks for the answer.