So every bike is different and I'm going to go over exactly what makes up my bike.
First we have the shifters. The shifters can control the braking as well as the shifting. The right shifter controls the rear derailleur. The left shifter controls the front derailleur. The right brake controls the rear brake. The left brake controls the front brake.
We also have peddles. These are called clipless pedals. They secure into your shoe with a specific cleat. Road bikes usually start at around 18 pounds. They're going to go down to about 14 pounds. You want a bike that's going, if you want to start racing you're going to want a bike that's between 14 and 17 pounds.
Wheels are very important. They reduce weight. Wheels are going to range in weight from around 1080 grams to 1800 grams. Again, wheels make a very, very big difference in regard to the weight of a bike. I highly recommend lighter wheels if you can afford it.
This is the saddle. It looks very small. It's usually paired with a cycling short which has a pad in it to make it more comfortable. Saddles are very unique to the rider. Some people find one saddle really comfortable while others find it completely uncomfortable. It's a trial and error sort of fit where you usually have to try out a number of different saddles before you can find the right one that fits you correctly.