Image description:
Picture with a slightly run-down looking church's front door on the right side of the picture, and on the left a section of the church's wall and a graffiti-covered dumpster in front of it.
On the wall is graffitied a 4x4 table with the columns labeled from left to right "M", "F", "N" and "PL" – for the masculine, feminine, neuter and plural forms. The rows are labeled from top to bottom "nom", "akk", "dat", "gen" for the nominative, accusative, dative and genetive cases. The corresponding definite articles are written out in the table each in its own spot (I hope screen readers don't barf with tables):
| M | F | N | PL | |
|---|---|---|---|---|
| NOM | DER | DIE | DAS | DIE |
| AKK | DEN | DIE | DAS | DIE |
| DAT | DEM | DER | DEM | DEN |
| GEN | DES | DER | DES | DER |
To be honest, I have no idea how anyone can memorise that. As a native speaker you hardly ever really think about it, you just know. But looking at the table it just seems like complete chaos, even to me.
Use it in a 1000 sentences each.
I barely speak German, but I do speak Polish where there are 7 cases, and it's just "how things are". Sometimes you stop to think about why, and it feels kind of surprising.
Then, I also speak¹ Basque, which has 17 cases... let me illustrate:
...that's the easy part, before verb conjugation:
(non-exhaustive table for just the regular helper verbs)
¹ "speak" as in only having to look up the tables from time to time.