Seems like the English here should be " I am eating many apples"... --- Or the actually useful sentence of "I eat many apples". Duolingo has a habit of using verbs in the Progressive forms (I am <verb>), and that is seldom the useful version in English. Also creates confusion for trying to learn to use "Ich bin <verb>" auf Deutsch
In general, you just have to learn which word uses them, I'm afraid. Try to view it as a separate letter, just like B is different from A, so is Ä different from A. Maybe not so much visually, but it always is in sound.
As far as the apples, there are many words that use A, AU, U, O in the singular, but change in the plural. When this kind of change is applied is not regular, so you'll have to learn that along with the words. Here are a few examples:
der Apfel, die Äpfel [the apple, the apples]
die Maus, die Mäuse [the mouse, the mice]
das Haus, die Häuser [the house, the houses]
der Fluss, die Flüsse [the river, the rivers]
der Ton, die Töne [the sound, the sounds]
Moreover, "Umlaute" are often used with the diminutive form of a noun:
der Apfel - das Äpfelchen [the apple, the little apple]
die Maus - das Mäuschen [the mouse, the little mouse]
das Haus - das Häuschen [the house, the little house]
der Fluss - das Flüsschen [the river, the little river]
der Ton - das Tönchen [the sound, the little sound - when it's really quiet, short, high-pitched, etc.]
Maybe this gives you some idea of what's cooking. :-)
Viele translates as 'a lot' or 'lots of' etc. While in some ways they can be synonyms, they are still different words. Several implies a more specific number: for instance, it wouldn't be more than 6. Whereas 'a lot' is less specific, so they are different words with slightly different meanings. Duolingo is about training you to understand the exact translations of each word so you can better understand the language! :)
If I'm wrong I hope I'm corrected. I think viel=much, as "wie viel kostet es?" How much does it cost?
Viele=many, as in the example duolingo gives in this problem. You wouldn't say "Ich esse viel Äpfel" because that means "I eat much apples."
Hope I helped and I hope I'm right!
I'm afraid that's a little wrong. Both viel and viele have the same meaning, but the ending changes according to whether it's referring to something masculine, feminine, neuter, plural, singular etc (and also according to the case such as accusative, dative etc!) It sounds complicated, but you do get used to it. All plural things take a feminine ending, which is -e. So here, because you're talking about multiple apples, it's the plural version of 'viel', which is viele. It means that it's often viele because the word often refers to something plural. Hope that helps!
Someone further down posted a helpful link of all the inflections. It's in German, but you can see the way it changes according to gender and case. http://canoo.net/inflection/viel:A
Äpfel is the plural of Apfel. The umlaut on the a (the double dot thing) is what makes the difference and it's pronounced slightly differently too. In 'apfel' the A has a normal 'a' sound, whereas when it's an Ä (as in, with an umlaut) it makes an 'e' sound. Someone wrote a comment above about the way they're pronounced.
To type umlaute using the US International Keyboard layout, type a quotation mark (") and then the letter over which you would like the umlaut to appear, i.e. a, A, o, O, u, or U. Nothing will appear on your screen when you type the quotation mark; once you type the a, o or u, the umlauted ä, ö or ü will appear.
You're right: Ich does only = I. It's the 'esse' that translates as 'am eating'.
In German, they don't have the two ways of using present tense that we have in English: the present and the present participle -- fancy terms for the difference between 'I eat' and 'I am eating'. It means that any present tense verb can be translated into either the present (I eat) or the present participle (I am eating).
So 'Ich sehe' could translate to either 'I see' or 'I am seeing'. 'Ich trinke' = 'I drink' or 'I am drinking'. They are interchangeable and both are marked correct on Duolingo. So this sentence could be both 'I eat lots of apples' and 'I am eating lots of apples' because of the verb, not the 'Ich'.
I hope that helps!