Although we don't use them in English, cases are really important in German!
Every noun/pronoun in a German sentence is in a particular case, depending on its function in the sentence.
There are 4 cases – The Nominative, The Accusative, The Dative and The Genitive.
I am going to teach you how to use The Nominative Case:
The SUBJECT of a German sentence i.e the person/thing in charge of or doing the verb is in the nominative case.
e.g. Ich wohne in England. I live in England.
(In this example ‘ich’ is in the nominative because it is the SUBJECT of the sentence. The pronoun ‘ich’ is in charge of/doing the verb ‘wohnen’.)
The Nominative Case is also used after the verbs:
bleiben (to stay), heiβen (to be called), scheinen (to seem/shine), sein (to be), werden (to become)
e.g. Sein Vater ist mein Lehrer. His father is my teacher.
(In this example ‘sein Vater’ is in the nominative because it is the SUBJECT of the sentence AND ‘mein Lehrer’ is also in the nominative because it comes after the verb ‘sein’.)
In the three other cases, articles may be declined (change form), however the nominative case is the only one where they do not change.
Here are the definite and indefinite articles in the nominative case:
Definite Article: Masculine – der (the) Feminine – die Neuter – das Plural – die
Indefinite Article: Masculine – ein (a/an) Feminine – eine Neuter – ein Plural – (k)eine