When I started my perfumery training, I started by learning my smells. Learning the smell and behaviour of the raw materials that are used to create fragrances; and I started with synthetics as it is simpler that way. The smell and behaviour of a synthetic chemical is far less complex than that of an Essential Oil, as an oil is, in itself, a complex mixture of chemicals. An Essential Oil can be thought of as a natural fragrance.
I don't think it matters whether you start with all base notes, or all top notes or a mixture of all three types. You should follow the behaviour of the individual chemical over hours, and even days; you will soon find out whether a particular chemical is a tiop note or not.
From memory (and it is a long time ago) we started with about 20 chemicals. I'll try to remember what they were, in no particular order:-
Phenyl Ethyl Alcohol
Hexyl Cinnamic ALdehyde
I'm afraid I can't remember any others. They are a good start. Try to describe them in your own words, and it doesn't matter how daft the description. If that's what you think it smells like then that's fine. Only when you are familiar will all of thee should you refer to the "official" description. It takes time.
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Once you have become familiar with these materials and are happy that you know what they smell like. You can think about getting some more, and also getting some Essential Oils. Make notes. Do whatever it takes to become familiar. You can also start making simple mixtures to see what happens. It is all very exciting, and interesting. Enjoy.