Arabic nouns are either masculine or feminine. Usually when referring to a male, a masculine noun is usually used and when referring to a female, a feminine noun is used. In most cases the feminine noun is formed by adding a special character, the ta marbuta ـة ة, to the end of the masculine noun.
Feminine Singular Masculine Singular
colleague زميلة زميلٌ
muslim مسلمة مسلم
thinker مفكّرة مفكّر
translator مترجمة مترجم
(someone sent on a mission) مراسلة مراسل
writer, author مؤلفة مؤلف
Sometimes the noun used to refer to a male and the noun used for a female are completely different.
It's not just nouns referring to people that have gender. Inanimate objects (doors, houses, cars, etc.) is either masculine or feminine. Whether an inanimate noun is masculine or feminine is mostly arbitrary. A lot of inanimate nouns ends in ta marbuta. When this is the case you know it is feminine.
Unfortunately, not all feminine nouns end in ta marbuta. Whenever you learn a new word, and that word is a noun, it's best if you learn it's gender too. Here are some masculine nouns..
book كتاب nose أنف
and here are some feminine nouns..