Properly Adjusting Front Derailleur

As the title suggest im fairley new to my road bike that I purchased one month ago, The bike i own is a fuji newest with tiagra components, I brought the bike back because the front derailer wont line up with the sprockets when i try to shift it so the chain just scrapes and hangs. the lbs said just a minor adjustment and its fixed but the problem is reacurring, Can some one please explain to me how to adjust this/ why this is happening. Thanks
Magix Puma

 

http://sheldonbrown.com/derailer-adjustment.html

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