What happens in velodrome?

So, what exactly goes on in a velodrome? It's a fascinating venue, but for those not familiar with cycling, it can be a bit of a mystery. Is it just a giant, circular track where cyclists go round and round? Or is there more to it than that? How do the races work? What kind of bikes do they use? And what kind of skills and training do the cyclists need to compete at the highest level? I'm eager to learn more about this exciting world of cycling in the velodrome.