The idea is to climb shorter, trickier routes, which are often called "problems." Because you're not tied in, you have a lot more freedom to move, which makes it a great way to work on your technique and get a fantastic full-body workout at the same time.
One of the best things about bouldering is how sociable it is. It's great fun to go with a group of mates and work on the same problem together, but it's just as good on your own if you just want to focus. With different graded routes all on the same wall at indoor gyms, there's always a new challenge waiting for you, whether you're a complete beginner or a seasoned pro.