The role of a ranger

[Mordyth]

Hi guys
Wondering if someone can give me some insight to the ranger class. I understand the roles of a monk in a group, as well as those backstabby rogue guys, but I dont understand how rangers fit.
Is their damage comparable to monks or rogues? Do they make up for it some other how? Buffs/some heals?
What am I missing with my understanding of the class?

Please note, this is not to be offensive to anyone who plays a ranger, I just dont get the usefulness of them in the game