Nouns are most often preceded by either a definite article (der, die, das: the) or an indefinite article (ein, eine: a/an). Whether to use a definite or an indefinite article in German is very similar to how you would use them in English:
Ein Frosch ist ein Tier.
A frog is an animal.
Der Froschkönig will eine Prinzessin küssen - irgendeine Prinzessin!!!
The frog king wants to kiss a princess - any princess!!!
As in English, there is no indefinite article in German in front of plural nouns because there is no plural form of the indefinite article (i.e., just like in English you couldn't say "a kings" or "a dwarves," you can't say "ein Könige" or "ein Zwerge" in German). Thus, you just let the noun stand on its own:
Könige haben Königreiche.
Kings have kingdoms.
Zwerge gibt es oft in Märchen.
There are often dwarves in fairy tales.
definite articles
indefinite articles
masculine
der Prinz (the prince)
ein Prinz (a prince)
feminine
die Prinzessin (the princess)
eine Prinzessin (a princess)
neutral
das Märchen (the fairy tale)
ein Märchen (a fairy tale)
plural
die Zwerge (the dwarves)
--- Zwerge (dwarves)
No articles
German typically does not use an article with predicate nouns (e.g., he is a prince, his name is Egon, etc.)
1.
a personal name
Der Froschkönig heißt Egon.
The frog king is called Egon.
2.
a major holiday
Ostern feiert der Froschkönig nicht; er mag keine Schokolade.
The frog king doesn't celebrate Easter; he doesn't like chocolate.
3.
the name of a country
Die Märchenfiguren leben in Deutschland.
The fairy tale characters live in Germany.
4.
a profession
Schneewittchen ist Studentin; sie studiert Jura.
Snow White is a student; she is studying law.
5.
a nationality
Der alte König ist Deutscher.
The old king is a German (man).
6.
"some" or "any"
Die böse Königin kauft Äpfel.
The evil queen buys (some) apples.
Exceptions of country names
While most countries are used without definite or indefinite articles, there are a handful of countries and regions, which use an article (this is not an exclusive list):