Here is a good story about track day insurance and a good source reference. There are others on the web.
Of course, Step 1 is to read your own policy to see what it actually covers.
Step 2 is to actually do Step 1. Don't just ignore it.
A driver should also consider whether you can afford to write off your car completely in the case of an accident where you're not covered - this is best done BEFORE you go to the track!
This type of insurance only applies to high performance driver's ed events (HPDE); typically a time trial or a wheel to wheel race is considered a "competition" and isn't covered - but this can vary. Again, read the fine print to find out what is defined as a "competition".
In wheel to wheel racing, the gentlemen's agreement is that everyone is responsible for their own car and has no liability to another driver. This means that if Driver 1 does something stupid, hits Driver 2, and Driver 2's car is totaled; Driver 1 has no financial responsibility. In reality, many drivers will take responsibility and help pay for damages that they caused but it is not required.
Odds are your insurance policy doesn't apply at the track. Here's what to do about it.