The cases: who did what to whom

The four jobs

Those are the masculine forms only. The pages for der, die and das carry the full set for every gender and the plural, and the guide to German articles explains why three letters are doing this much work.

Look at the English column. Two of those four are handled in English by a preposition - to, for, of - and the other two by position alone. German does all four with an ending. That is the trade the language runs on: fewer small words, more information per word.

Nominative and accusative first, because they change meaning

These two carry the most weight for a beginner, and the contrast between them is where German sentences stop looking arbitrary:

Der Mann sieht das Kind. - The man sees the child.

Den Mann sieht das Kind. - The child sees the man.

Identical words. Identical order. Opposite events. The only difference is der against den, and if you are not reading the article you are not reading the sentence.

It also works the other way. Both of these mean the man sees the child:

Der Mann sieht das Kind.

Das Kind sieht der Mann.

A German writer picks between them for emphasis, or rhythm, or to land a particular word at the end. English has to rewrite the sentence to do the same job. The end of the clause is prime territory in German: it is also where a modal verb sends the verb it is colouring.

Dative arrives sooner than you expect

Dative is the recipient: the one something is given to, said to, or done for.

Ich gebe dem Kind Zeit. - I give the child time.

Here Zeit is what is given (accusative) and dem Kind is who gets it (dative). English marks exactly the same distinction, just with position and the word to.

The reason dative cannot be postponed is prepositions. A large group of the commonest ones - mit, von, zu, nach, bei, aus - always take the dative, with no exceptions to learn. So mit dem Kind, von dem Mann, zu dem Haus. Meet those prepositions, and you have met the dative whether you planned to or not.

The practical order

1. Nominative and accusative, as a pair, because the contrast is what changes meaning.
2. Dative, driven by the prepositions that demand it rather than learned as an abstraction.
3. Genitive, recognised before it is produced.

And one habit underneath all three: when a German sentence looks like a jumble, do not translate left to right. Find the articles, work out which noun is doing the verb, and read outward from there. That is not a trick for beginners. It is what reading German is. When you want to practise that on real sentences, the German course is where the articles and pronouns above get drilled.