Arabic words are either masculine or feminine. For example: رجل (ra-jul) which means man is masculine.امرأة (im-ra-ah) which means woman is feminine. These two examples are very logical. But just like many other languages, everyday objects have their own gender as well. For example the word for ear, must be either masculine or feminine.
The most common way to tell a masculine word from a feminine word is the ة (taa' mar-boo-Tah). If a word ends in a ة (h/t) then it is most likely feminine. To make a masculine word feminine usually a ة (h/t) is added to the end of the word.
female dog, she-dog
In Arabic nouns, as well as adjectives, have to agree in gender, as well as number.
The boy is big
The girl is big.
Did you notice that we called the girl "big" with كبيرة (ka-bee-rah) while when we want to say the boy is big we said كبير(ka-beer). This is generally how it works for singular nouns.
The boy is small
The girl is small.
الولد قصير والبنت طويلة
al_waladu qaSeer wa al_bintu Taweelah(-tun)
The boy is short, and the girl is tall.