How do I discipline adults?

[It's Easy]

I work at an adult residential treatment center for substance abuse and I'm having a hard time disciplining the clients. There are so many silly but important things they cannot do like reading a trendy magazine. I'm 23 and some of them are close to my age. It's even harder with the ones older than I. I'm completely new to this and I am sort of an intern so I'm learning the ropes and its difficult. When I think about it I'm confident its just when it comes down to the real situation I have a hard timet being in control