First of all, both of you need the equipment shown in the HT5887 article above. Older iPads, iPhones, etc. are not capable of AirDrop.
Second, you need to be trying to share non copy-protected information. For example, you would not be able to share music purchased through the iTunes Store, as the other person does not own the music.
So if you meet all the prerequisites, follow the instructions in the HT5887 article you attached.