What does being a vegan mean?

Hello :), im curious about what being (a) Vegan really means. I'm 14, overweight, and don't just want to go on a diet, but make a lifestyle change. I've been very depressed, and, as a result of that have had BIG self-esteem problem. I mean BIG. Its really important to me that i do this for myself :). I've also had a history of eating disorders, & would like to make sure that this is SAFE for me to do. So, i have some questions.... Is it like being a vegetarian to the extream?? Like, i've heard that they cant have dairy? Is this true? ANY other input would be AMAZING!!! :D