1. Noun Genders

Three Genders: German nouns have three genders: masculine (der), feminine (die), and neuter (das).
Gender is Not Logical: Unfortunately, there's no easy rule to determine a noun's gender. You generally need to memorize them. (https://bit.ly/3Zs0vqv)
Examples:
Der Tisch (the table - masculine)
Die Katze (the cat - feminine)
Das Buch (the book - neuter)
2. Cases

Four Cases: German has four cases: Nominative, Accusative, Dative, and Genitive.
Case Affects Articles and Nouns: The case of a noun affects the article (der, die, das) and often the form of the noun itself.
Example:
Nominative: Ich sehe den Mann. (I see the man.)
Accusative: Ich sehe den Mann. (I see the man.)
Dative: Ich helfe dem Mann. (I help the man.)
Genitive: Das Buch des Mannes. (The man's book.)
3. Verb Conjugation

Present Tense: Verbs change their endings depending on the subject (ich, du, er/sie/es, wir, ihr, Sie).
Example:
Ich spreche Deutsch. (I speak German.)
Du sprichst Deutsch. (You speak German.)
Er/Sie/Es spricht Deutsch. (He/She/It speaks German.)
4. Word Order

Basic Structure: Subject-Verb-Object (SVO) is the most common word order.
Example: Ich lese ein Buch. (I read a book.)
Variations: Word order can change in subordinate clauses and questions.
5. Adjective Endings

Agreement: Adjectives agree with the noun they describe in gender, number, and case.
Example: Der gute Wein (the good wine)
These are some of the most fundamental grammar rules in German. Mastering these will lay a strong foundation for your German language learning journey.