The Learning System
It's a tiny bit annoying to be given exercises without being given a lesson first. I already know a little French so it's not such a big deal for me, but sometimes you can't correctly translate a sentence into English just based on the given translations of new words. For example, in 'Elle est une femme de ménage', you are only given the translation of 'ménage' and are forced to guess what 'femme de ménage' means. Also, I've only gone through units with the present tense, and there are sentences with the past tense which, again, we're forced to translate by guessing. So I think it would do us all some good to have actual lessons in vocabulary and grammar before doing the exercise units. I realise it's a lot to ask, but it's either that, or Duolingo must be used together with a more comprehensive language learning site for a complete learning experience.
@Terrafora "nous mangeons", and note that it's pronounced "manj-on"--the vous form is "mangez," pronounced "manj-ay," but you're right that the others are pronounced "manj." The pronunciation rules here come more from the general French habit of dropping terminal consonants than from anything to do with the verb specifically--with other verbs, the pronunciation can change quite a lot depending on the conjugation.
@Everyone, until they start adding grammar lessons (and I really hope they do) using another resource for grammar is a really good idea. My favorite sites are http://french.about.com/ and http://www.laits.utexas.edu/tex/index.html . There's also a book called French Grammar by Christopher Kendris, published by Barron's, that I think would be a really good complement to this site--it's a reference book rather than a textbook, so it's cheap, and it has good, technical explanations of just about everything this site covers. Taking a class is also a great idea, if you can--try your local community college. (I know, I'm old-fashioned... ^^; )
http://www.laits.utexas.edu/tex/gr/v1.html This is the UT Introduction to Verbs with some more information about conjugation.
In reply to Saio, French seems to change the spelling of words based on which party is addressed while not changing the pronunciation of the word so manges will change multiple time depending on the party it reference, examples would be: tu manges je/il/elle mange, les mangent, nous mangens etc. This can be incredibly discouraging at first and it's made harder by the fact that there isn't really any context for these sentences when all we're given is an audio clip. But don't lose heart. Trial and error is probably the best way to learn most things in life. just keep an eye out for the patterns for when which spelling is used where. You could do what I do and write down the words and their meanings as you encounter new words or spellings and jot down the context of them for future reference. Regardless, somewhere down the line if you keep up with the studying it'll all fit into place and you'll simply understand it without having to really think too much about it.
If you want a more structured lesson plan, have a look at the UK's BBC website: http://www.bbc.co.uk/languages/french/ I'm not sure if video materials can be accessed from outside the UK. However, there are several courses here for different stages and ages, all with transcripts. They are often used in schools, so make sure you read the comprehensive teacher's notes that give good explanations of why a particular word or phrase is used. E.g. for "parler" >>> If you speak a language well, say je parle bien, fluently is couramment and if you speak just a little, say je parle un petit peu.
If you want a word spelled out say Ça s'écrit comment ? (how is that written?). The verb écrire means 'to write' and here it is turned into a reflexive verb, so the phrase literally means 'how does that write itself?' You might also want to ask how something is pronounced: Ça se prononce comment ? <<<
@anomalocaris I agree with you there. Nothing beats a classroom setting when it comes to learning a language (except actually practising in the country of the language of course). I was thinking about taking French lessons but I'm already doing Japanese lessons at the moment and making that kind of commitment may be a little much at the moment. :/