iPad error adding the purchased files on the device

Hi there,
The problem is that I have bought some files form Store and now it seems like I cannot use them after I pay. Is for the first time when I have this error and hope I waste some good money. Please help me to solve this. What I did wrong and why the triangle below the error is not helping ?
Thank you !

Some of the purchased items on the iPad "[email protected]",including "Cigar Boss
HD", could not be transferred to your iTunes library because you are not authorized for them on this
computer.
To authorize this computer for items purchased form the iTunes
Store, choose Store > Authorize This Computer.
For a list that could not be transferred, click the triangle below.
