Promener is a pronominal verb that requires a reflexive pronoun.
It is a "learn by doing" philosophy. I suspect the rationale is that you can get very overwhelmed by reading lots of grammar rules (and if they're present, one may feel they have to read them), but that if you simply use the language enough, the correct grammar will begin to "sound right." This is like how many native English speakers may not explicitly know the rules of grammar in English, but they use them perfectly well when speaking.
I think it does the opposite. While I don't like learning a bunch of grammar rules at once, I think it would be nice if they were more easily accessible - like if there was a built-in way to see tips or rules directly related to each individual exercise rather than having to go read the entire set of tips at once to find the one bit of info I wanted for clarification. Comments and forum posts work pretty well, but the quality of explanations varies, and it would just be nice to have them as a built in feature.
The problem with that is that nothing gets explained. I wouldn't be past level 2 of French on Duolingo if I didn't take French at my school. (I know because I tried this before high school and hated it, because nothing was ever explained) That's my rationale, and it's quite rational if you ask me
The German version offers far more help than the French. In German it actually has brief grammar lessons that I found to be just about the right length. Here there are none, and it's very frustrating -- I cannot thank Laura Lawless of about.com enough, nor the people who keep posting links to it here.
I appreciate @smearedink's comment on learning-by-doing; it's how I myself teach. But every bottom-up learning-by-struggling process must eventually be balanced by some amount of top-down teaching ("here are the rules") after a while: it's just good pedagogy.
"marcher" refers strictly to the action of walking, it has no extra information or subtext. It's literally "walking" . "se promener" , as DmytroShkr said, implies walking for a leisurely purpose, more closely translated as "taking a walk" , which could also be said "prendre une marche" in french. "prendre une marche" and "se promener" are very close in meaning, but I'd say that "prendre une marche" implies a path of some sort, i.e. I'm going to start here, walk along here, and end up back here. Whereas "se promener" is usually aimless. "Je me promène au centre ville" (I'm walking downtown) doesn't tell you that I'm walking to a particular place downtown, or taking a certain path.
I wouldn't ignore it. I would take a note and try to remember that this is a feature of the French language. Otherwise you might forget it if you have to translate a verb like this into French. For me it helps to remember two translations for constructions like this: A "good translation" that makes sense in English ("You are taking a walk") and a "bad translation" ("You take yourself for a walk"). I often try to picture the latter one to make it more rememberable. ("You leisurely walk on the footway, hand in hand with yourself.") ;)
For walking dogs you'd use «promener le chien» or «sortir le chien» (more rarely).
http://dictionary.reverso.net/english-french/walk%20the%20dog -- example sentences at the bottom.
Yes, this is how reflexive verbs work. Take a look here: http://french.about.com/od/grammar/a/pronominalverbs.htm
I am on a lesson where the latest example is "Vous vous promenez. Ne vous promenez pas" and it translates to "You AREN'T going for a walk. Don't go for a walk". I get why the second half of the sentence is negative, but why is "vous vous promenez" suddenly "you aren't", I would think it's "you ARE going for a walk". I don't see any negatives in there