So a pack otherwise known as a peloton, is a group of cyclists that's usually between 20 and 100 cyclists and they ride in very close formation. The group is going to be staying together because it's a lot easier to ride in a large group. The reason cyclists ride in a pack is to protect themselves from the wind. It's going to be a lot easier to ride in someone's draft than to ride by yourself and push the wind out of the way yourself.
So when you ride in a group, cyclists can conserve energy and cover a greater distance a lot quicker. There is no leader to a pack. When you ride in a peloton, there's usually, it's a cooperative effort of riders going to the front, keeping the pace, setting a proper pace, and then pulling off and moving to the back. When you ride in a pack it's mutually beneficial for everyone to work together. The idea is to share the effort with a group of riders, being from a number of different teams in order to chase down people who are in front of you or in order to keep the pace at a certain level.
You're going to encounter packs or groups of cyclists or pelotons usually when the course is flat. So when the course is flat, wind plays a greater role in cycling. When you're going uphill you're going to be going at a slower speed, wind is not going to be playing as much of a factor. So, you're going to encounter riding in a peloton or riding in a pack more often. The peloton can stay together the entire race or if it gets incredibly windy or if it's very hilly it will break up and a break will form.
So you don't want to just jump into riding in a group of a hundred cyclists. The best way of doing it, the safest way, is to start riding by yourself. Get really comfortable riding for a long time at a nice, safe speed where you're not moving around a lot. After you're comfortable with that, you want to ride with a friend. You want to ride next to them, you want to ride behind them, you want to ride in front of them, you want to start learning how to draft right behind that person. You're going to notice that when you're riding right behind the person, that you're actually expending a lot less energy. About a third less energy. So you're going to start feeling that and you're going to realize the exact position you want to be in to conserve energy and go as fast as possible.
Once you become comfortable riding with just one other person, the next step is riding in a smaller group. This is still not a pack. It could be four or five riders. Once you're comfortable doing that, then you can start riding in a larger group. So it's sort of a linear development. You want to start really small, ride by yourself, get really used to riding your bike for a long period of time. Then ride with a friend, get used to riding next him, riding behind him, riding in front of him. Move into a small group, get used to the group dynamics, slowing down, speeding up, holding a very steady pace within the group. And then finally, you can join a large group of cyclists and enjoy riding in a pack.