add ـونَ (ūna)
Used for male people / groups
Examples
مُدَرِّس (mudarris) → مُدَرِّسُونَ (mudarrisūn)
teacher/teachers
Grammar reference / Plural forms
Plural forms (الجَمْع)
The three ways Arabic forms plurals: two predictable “sound” patterns plus the “broken” pattern that has to be memorised word by word.
add ـات (āt)
Used for feminine nouns & many objects
Examples
مَكْتَبَة (maktabah) → مَكْتَبَات (maktabāt)
library/libraries
change inside the word
NO single rule so you must simply memorise the words
Examples
قَلَم (qalam) → أَقْلَام (aqlām)
pen/pens
دَرْس (dars) → دُرُوس (durūs)
lesson/lessons