IF you really wnt to become knowledgeable about the audio world, you are going to need to learn a lot. IT is a lot of reading, a lot of observing, a lot of hands on experience (if you can). It takes a lot of time, so please, do not get frustrated by the amount of information that I am about to post, because this is where to start if you really want to learn, and boy is there a lot to learn.
These first two links are a good generalization of what common terms mean. To get a better understanding of what they actually mean (the links are lose definitions) to the people in the field, you are going to need to get a good understanding of the sound of a lot of different things. In my experience, good understanding of the terms came best with good understanding of reviews and whatnot, but this is a good place to start. Remember, fast a lose.
http://www.head-fi.org/a/describing-sound-a-glossary
http://www.head-fi.org/a/glossary-of-terms
This man, |joker|, is a very well respected reviewer. He has reviewed hundreds of iems and portable headphones. If he says something, you need to listen. Now, not everyone will have the same opinions, everyone hears things differently, and everyone has a sound signature that they prefer (he like a colder, more analytical sound in general), but he is honestly one of the most objective reviewers that I have had the fortune of reading. You ought to give his opinions a good amount of weight.
http://www.head-fi.org/t/478568/multi-iem-review-328-iems-compared-lear-luf-4f-luf-4b-luf-4c-added-11-07-14-p-994
http://www.head-fi.org/t/433318/shootout-113-portable-headphones-reviewed-alpha-design-labs-adl-h118-added-07-15-14
CliOS is another reviewer who commands respect to a similar degree as |joker|. Take his opinions very seriously.
http://www.head-fi.org/t/541204/concise-multi-iem-comparison-final-update-march-1st-2013
http://www.head-fi.org/t/596482/the-sub-100-portable-amps-shootout-11-1-amps-compared
http://www.head-fi.org/t/620775/the-sub-200-portable-amps-shootout-13-11-amps-compared
This website is a really good place to find some solid information. I like the graphs and whatnot that they make (I like frequency response graphs a lot), but their reviews I find somewhat questionable. That is that problem that I have with most "review sites". They are usually getting the headphones or whatever from the company, so there is a bit of a conflict of interest and since audio is all subjective reporting, it makes things a bit questionable. That said, I like their reviews a lot, I just like user review (on sites like head-fi) better. Tyll does have a favored sound signature, but I don't know what it is (I am more familiar with |joker| and his reviews).
http://www.innerfidelity.com/
Some of the best place to get information is just from users who happen to have the equipment that you are interested in. So, for example, if you want to know how two headphones compare, and there is no thread or review already up which compares them (and they don't have very different sound signatures which would give you a good idea of how they sounded right off the bat), then you could pm a user on head-fi (or maybe start a thread) and ask them straight up. Try not to be annoying though. People only have so much patience, so try not to ask anyone any questions which you can find the answers to somewhere online (becuase why ask a question which has already been answered?). So yeah, research a TON first, but do remember that you can just ask people if you need to.