Hi,
Intermediate S2 Lesson #13 contains an overview of declensions, and in Intermediate S3 Lessons 10, 11, 14, 15 and 20, 21 we explain each case and its changes in great detail.
In short, there is a concept of key endings and bland endings. For every case there's a key ending, such as -er for masculine Nominative singular (yielding "der", "neuer", "Deutscher", etc.) or -e for Nominative & Accusative plural for all genders (yielding "die", "neue", "Deutsche", etc.). These key endings are important for comprehension and won't typically be slurred in speech, unlike the bland endings. However, when you have a line of words that could each take the key endings, for example article + adjective + noun, only the first suitable word gets the key ending and the others will adopt a bland ending, which is usually -en or -e (it depends on the case). Hence we'd say "DER neue Bond Film" or "Ein neuER Bond Film" - in the first case, "der" takes the key ending and "neue" gets a bland ending; in the second case "einer" isn't a valid masculine form, so the key ending is only used on "neuer".
Nouns such as "Stimme" and "Film" don't change according to the declensions; they just have one form for singular (Stimme, Film) and one form for plural (Stimmen, Filme). However, there are a few types of nouns that add endings much like articles and adjectives, for example nouns ending in -er.
3. Hmm, nicht schlecht, aber mir wäre eine Komödie lieber, etwas lustiges. Why don't you need the word es after the word aber?
"eine Komödie" is the subject. The sentence could be "Eine Komödie wäre mir lieber"; "es" doesn't make sense to add to this sentence. We just change the word order in order to emphasize that IN MY OPINION a comedy would be better.
I hope this helps!
