noun
class
A1
Klasse (die, plural: Klassen) primarily means 'class'—a school group or course, or a category/grouping (social or quality, e.g. first class). It's a regular feminine noun with standard plural 'Klassen'. No special prepositions; used like other nouns in constructions (e.g. in der Klasse, eine Klasse besuchen).
Examples
Die Klasse beginnt um neun Uhr.
The class starts at nine o'clock.
Ich bin in der Klasse.
I am in class.
Der Lehrer lobte die Klasse, nachdem die Schüler die Prüfung bestanden hatten.
The teacher praised the class after the students had passed the exam.
Details
Mnemonics
A classroom full of students with a sign 'Klasse 1A'
sounds like English 'class' — same idea
Notes
'Klasse' can also be used colloquially to mean 'great' (Das ist klasse!).