In Arabic a word can represent either one of something (singular), two of something (dual), or many of something (Arabic plural, three or more).
This page is about how words go from being singular to plural in Arabic.
Regular Feminine Plural
A feminine noun is usually made plural by adding ات (alif then taa', pronounced -aat), to the end of the word.
mughaamarah (pausal form)
mughaamaratin (genitive or preceded by a preposition)
All of these mean "adventure" and all become:
Regular Masculine Plural
A masculine noun is usually made plural by adding at the end of the word ون (waw then nuun, pronounced -uun) for the nominative case, and ين (ya' then nuun, pronounced -iin) for other cases.
- مسلم ---> مسلمين
Muslim ---> muslimiin (pausal form)
- مسلمٌ ---> مسلمون
muslimun ---> muslimuun (nominative)
- مسلمً ----> مسلمين
musliman ---> muslimiin (accusative)
- مسلم ٍ ----> مسلمين
muslimin ---> muslimiin (genitive or preceded by a preposition)
All of these mean "muslim(s)"; note that the last two forms have the same plural.