I am learning Drupal 7 and want to know the way to learn modules
I think the most important is experience. Just installing and enabling some modules, trying them out gives you a feeling of how things work. There are many youtube videos that show you exactly what to do. But I can't stress this too much: experience is what we need. Don't make the same mistake as I did in the beginning when I studied more than I tried.

Don't be afraid to try things out, even if they don't seem to work in the beginning. Be persistent and follow the guidelines out there. Should you need specific advice on a module, feel free to ask here or in drupal.org where you should become a member. (if you are not already!)

I don't think there is an "officially correct way to learn". If there is, then I bet it is called persistence! So get involved and see you out in the field :D.