Just bring a picture of Justin Bieber showing the cut that you want and ask for it. The hairdresser will base your haircut from the picture. But honestly, a lot of guys have that hairstyle.
Here's a good picture of Justin Bieber's haircut:
I was always curious about the name of Justin Bieber's haircut. Most sources seem to call it the"fringe" or the "flow", but then when you search those hairstyles it's all women.
Some hairstyle tips: Justin Bieber's hair looks naturally straight, no need for straighteners. Do comb, not brush. Combing your hair will give you that sleek, shiny look. Use shower conditioner, but don't over do it. Before you go to bed wear a beanie and turn it a little bit, to which ever side you want your bangs to be sweep.
Here's Justin Bieber explaining how he does his hair every day, not exactly a how to video tutorial but you get to see how it's done.