I've been here a long time and I'm still realizing that there are so many people here with a lot more knowledge on the subject of fragrances.
I don't really get a chance to do this but I just smell around and test fragrances. It gives your nose "practice" and your memory a more vast selection of fragrance qualities. You'll start realizing similarities and differences based on the notes, and eventually you'll be able to name those notes you are smelling. It is practice/constant training of your nose.
To find the different layers of fragrances you generally go by this: First 1 hour is the maximum time for the first layer, usually. Most times it's the first 15 mintues for me. You'll notice the scent changing. Then the middle notes will last for a few hours. After about 2-3 hours of wearing the scent you are in the basenotes. This is an approximation of what I experience and have heard. I hope it helps.