How do you get into this sport? You just did it. Congratulations.
Bike racing is a tough sport. Fitness is a huge barrier to entry and its not a sport where the novice level is easy. Ride with the local fast guys, and find group rides that are challenging. Get advice from them (or here) learning a bit will be able to help you cheat fitness (via drafting and smarter choices) but mostly ride fast a lot.