Nouns

However, there are exceptions. All of these words are feminine, even though they don't end in a ta marbuuTa:

نار (naar) fire
سما (sama) sky
أرض (arD) land/earth
شمس (šams) sun
ريح (riiH) wind
عين (3ein) eye
يد (iid) hand
روح (ruuH) soul
حرب (Harb) war

Nouns that can refer to both men and women (like job titles) can be made feminine with the addition of the suffix ـة (-a).

               Masculine            Feminine
teacher مدرس (mudarris) مدرسة (mudarrisa)
engineer مهندس (mohandis) مهندسة (mohandisa)
actor ممثل (mumassil) ممثلة (mumassila)
artist فنان (fannaan) فنانة (fannaana) 

Nouns: number

Dual nouns

In Arabic, if you're talking about two things, you need to use the dual form of the noun. Just add the suffix ـين (-ein) to the masculine singular form of the noun.

Singular                           Dual
book كتاب (kitaab) كتابين (kitaabein)
window شباك (šibbaak) شباكين (šibbaakein)

Note: If the singular form ends in a taa marbuuTa (ـة, -a), you need to "untie it" - change it to a ت - before adding the ـين suffix. Take the word جملة ("sentence") as an example:

جملة (gomla)
"Untie" the taa marbuuTa (replace it with a ت): جملت
Add the ـين suffix: جملتين (gomlatein) - "two sentences"

Note: While you can use the ـين suffix to talk about two people, usually it's better to say "اتنين (itnein) + [plural noun]":

                Singular                      Dual
teacher مدرس (mudarris) اتينين مدرسين (itnein mudarrisiin)
engineer مهندس (mohandis) اتنين مهندسين (itnein mohandisiin)

If you want to talk about a pair of things, like socks or shoes, you should use the singular form of the noun, and it'll be understood that you're talking about a pair. If you want to talk about one item out of a pair, say فردة من (farda min), literally "an individual from."

لازم اشتري جزمة جديدة (laazim ašteri gazma gdiida)
I need to buy a new pair of shoes. - Note that although "gazma" technically means "shoe," it's understood that you mean a pair of shoes.
أنا مش لاقية فردة من شرابي (ana miš la'ya farda min šaraabi)
I can't find one of my socks. - Again, note that "šaraabi" technically means just "my sock," but it's understood to mean a pair.

Regular masculine plurals

There are some nouns that have regular (sound) plurals. Almost all masculine nouns that have regular plurals fall under the category of job titles etc. that can refer to either men or a mixed group of men and women. To make one of these nouns plural, you simply add the suffix ـين (-iin).

                 Singular.                    Plural
teacher مدرس (mudarris) مدرسين (mudarrisiin)
engineer مهندس (mohandis) مهندسين (mohandisiin)
actor ممثل (mumassil) ممثلين (mumassiliin)
artist فنان (fannaan) فنانين (fannaaniin)

Note: In Arabic, plural human nouns that take the masculine form can refer to either a group of all men, or a group of men and women. So a group of مهندسين could be a bunch of male engineers, or a mixed group of male and female engineers.

Regular feminine plurals

To make a feminine noun (that doesn't have a broken plural form) plural, you drop the taa marbuuTa and add the suffix ـات (-aat). Many foreign loanwords, even some that are masculine, take this plural form (see جاكيتة and كومبيوتر).

            Singular.                 Plural
car عربية (arabiyya) عربيات (arabiyyaat)
word كلمة (kelma) كلمات (kalimaat)
clinic عيادة  (iyaada)  عيادات  (iyaadaat)
jacket جاكيتة (žakitta) جاكيتات (žakittaat)
computer كومبيوتر (kombiyuuter) كومبيوترات (kombiyuuteraat)

Note: If you want to talk about a group of all women, you take the masculine singular form of the noun and, again, add the ـاتsuffix.

                         Singular       Feminine plural
teacher مدرس (mudarris) مدرسات (mudarrisaat)
engineer مهندس (mohandis) مهندسات (mohandisaat)
actor ممثل (mumassil) ممثلات (mumassilaat)
artist فنان (fannaan) فنانات (fannaanaat)