Well arturopkmn...it's a story about love, deception, greed, lust and…unbridled enthusiasm.
You can read about it here:
After that, the answer you're looking for lies here (Specifically under "Indefinite articles"):
If you want the Coles' notes version, it is "einen" because it is in the accusative case.
Hope that helps, and enjoy the read.
No. No such rule exists in German (einen before a vowel).
There are four "cases" in German. Depending on what the case is, "ein" gets changed. Go to the two links I posted to learn about cases, and when "ein" becomes "einen".
I see that you haven't yet completed "Basics 1". When you complete it, you will have access to "Basics 2". The introduction to "Basics 2" has a write up on cases. Here is the link for it, but I'm not sure if you can access it without having reached that level.
If you can't access it, just finish Basics 1 and you'll be able to see it.
I hope that helps! If you still have trouble after the links, I'll try to answer your follow up questions if you want.
In German there are four major "cases": nominative, accusative, dative and genitive. ein (masculin a) is used in the nominative case. Nominative case is when the noun is the subject of the sentence e.g. Das is ein Apfel (that is an apple). You use einen in the accusative case which is when the verb is the direct object in the sentence. An example of this could be Ich habe einen Bruder (I have a brother).
Sie is also you, but "sie" is she/they and "Sie" is you. Since it is at the beginning of a sentence you can't look for the capital "S" to determine who it is, you have to look at the verb ending.
- Sie isst = she eats
- Sie essen = you (formal, singular or plural) eat, they eat (you need context to figure out which)
Hope that helps.
You use "einen" just like when you use "den." It depends if the noun is a direct object. For example, "I like pizza," "He builds a fort," "She drives the car." Pizza, a fort, and the car are all what the action happens to and so are all direct objects. Whenever the noun is a D.O., you use "einen" instead of "ein" or "eine" just as you use "den" instead of "der." In "Sie isst einen Apfel" the apple is the D.O., so "ein" becomes "einen." Hope this helps!
Mas. Fem. Neu.</pre>
Nom. ein eine ein
Acc. einen eine ein Dat. einem einer einem Gen. eines einer eines
In this case, Sie (She) is the subject (nominative case) and Apple is the direct object (Accusative case). Apple being masculine, "einen" will be used for it (according to the table of indefinite articles).
It'd be easy for you if you learn the grammar rules first. Hope this helps! :)
You use einen when the noun ia the one "receiving" the action.. For example what is beeing eaten? The apple and so on... Its named Akkusative in German.