I have a few friends that are vegans, do you know much about it?
Not much but I do know some people follow the diet or the philosophy or both.
I know there are different types of it, do you know about any of the types?
Common vegans are dietary vegans stop eating animal products like meat and dairy. 
What are the reasons behind becoming a vegan?
The main reason is that they believe its cruel. Also some extend the philosophy into other areas of their lives, and oppose the use of animals for any purpose.
Are there religious reasons as well?
Yes religious reasons do play into it but only for some. Some religions regard animals higher up than others. Also vegan diets help with reducing chronic disease like heart disease.