What are the effects of a broken leg?

I realize I wasn't very specific in the question. I'm very curious about the topic. You see, one of my friends broke their leg and had to use crutches. Nearly the same thing happened to one of my other friends, but she got to wear this huge boot, and she could walk around without crutches. Do you get the choice between a boot or crutches, or is there a certain number of days you have to achieve to get upgraded from a cast to a boot? Sorry if this question is stupid, but I'm not very knowledgeable on anything, well, medical. Any help would be appreciated. Also, what is the boot called? It encases the foot and the shin, and it's mive and black.