There is no difference -- the two look, sound, and smell the same.
Usually, you don't have to tell the difference anyway, since nearly always, only one gender will make sense -- and where it could make a difference (e.g. ein Tor, ein Laster), context will usually make it clear which meaning is meant -- just as with nouns that have more than one meaning but the same gender, or like someone who needs to buy "a new pen" in English: if it's a farmer whose pig just broke out of its enclosure, you'll understand it differently from if it's a schoolchild who can't write any more.
ein is used for grammatically masculine nouns (ein Mann "a man", ein Löffel "a spoon") as well as for grammatically neuter nouns (ein Kind "a child", ein Mädchen "a girl", ein Messer "a knife").
eine is used for grammatically feminine nouns (eine Frau "a woman", eine Gabel "a fork").
Note that all nouns have a grammatical gender, not just ones referring to humans, animals, or other living creatures (e.g. "fork" is feminine, "spoon" is masculine), and that grammatical gender and natural gender do not always match (e.g. Mädchen "girl" is grammatically neuter, Person "person" or Geisel "hostage" are grammatically feminine even if the person is male).
Also, those are the forms used in the nominative case, used e.g. for the subject of a sentence or coming after "du bist/ihr seid/er ist/...".
In other cases (e.g. the accusative for a direct object), the forms can change - but Duo will teach that when they come up.
Oh, okay. I see; personally I would round my lips like when whistling.
Du bist ein Kind = "You are a child".
I'd say that's the most accurate translation. It's the only one that comes to my mind - I'm not sure which, of any, "less accurate" but still valid translations you might be thinking of.
This is a fairly simple sentence and maps very straightforwardly to English:
- du = you (when speaking to one person whom you know well)
- bist = are (verb form for du)
- ein = a(n)
- Kind = child
du bist ein Kind = you are a child. You would use this form when you are talking to one young person (or one person whom you know well) and saying that that person is a child.
ihr seid ein Kind = you are a child. You would use this form when you are talking to several young people (or several people whom you know well) and saying that all those people together are one child.
ihr seid ein Kind doesn't make sense, because several people together cannot be one child.
Very theoretically, Ihr seid ein Kind could also be used if you are speaking to one person who is part of a royal family, and you are saying that this royal person is a child.
But in practice, this use of Ihr for politeness is pretty much extinct nowadays.
But depending on the grammatical gender of the thing you are talking about, it can also be er or sie.
For example, Was macht der Hund? Er schläft. Was macht die Katze? Sie trinkt. Das macht das Pferd? Es frisst. "What is the dog doing? It's sleeping. What is the cat doing? It's drinking. What is the horse doing? It's eating."
du bist is "you are" when you are talking to one person whom you know well.
ihr seid is "you are" when you are talking to several people whom you know well.
Sie sind (with capital Sie) is "you are" when you are speaking formally or politely, to a person or people whom you do not know well. (No difference between one person or many people here.)
sie sind is "they are".
Because it is a noun. All nouns are capitalised in German.
This is mentioned in the tips and notes for the very first unit... if you haven't been reading the tips and notes, I recommend that you start doing so.
For most users, they're only available on the website https://www.duolingo.com/ , not in any mobile app. Select a unit, then click on the little lightbulb icon in the window that pops up:
That is true, although pronouns can sometimes be confusing because they are not capitalized. Words like "ich", "er", "es", and so on are not capitalized (unless they are at the very beginning of the sentence), which sometimes confuses people. Also words used as placeholders, like "diese" to refer to "these".
Similar, yes - adjectives, articles, possessives etc. take different endings according to gender, number, and case of the noun they modify, if they are before the noun.
However, adjectives after "to be", near the end of the sentence, do not -- unlike Spanish.
So you have:
- der große Mann, ein großer Mann = the big man, a big man
- die große Frau, eine große Frau = the big woman, a big woman
- das große Kind, ein großes Kind = the big child, a big child
with endings but
- der Mann ist groß = the man is big
- die Frau ist groß = the woman is big
- das Kind ist groß = the child is big
bist is specifically for du (you, informal, singular), while sind is for wir (we), sie (they), and Sie (you, formal).
ihr (you, informal, plural) uses seid, for example, and ich (I) uses bin.
- ich bin
- du bist
- er, sie, es ist
- wir sind
- ihr seid
- sie sind; Sie sind
Because not every hint is valid in every sentence.
bist = "have" works in cases such as the past tense which is sometimes formed with "to be" in German but always with "to have" in English, e.g. du bist gekommen = "you have come".
But that "equivalence" does not work when the verb has its full meaning.