Meaning of yī:
一
one; single; a (article); as soon as; entire; whole; all; throughout; "one" radical in Chinese characters (Kangxi radical 1); also pr. [yao1] for greater clarity when spelling out numbers digit by digit
Wǒ zhǐ xūyào yī zhāng piào.
我只需要一张票。
I only need one ticket.
Tā zhǐ yǒu yī zhī māo.
他只有一只猫。
He only has a single cat.
Tā shì yí gè hěn hǎo de péngyǒu.
他是一个很好的朋友。
He is a very good friend.
Tā yī dào jiā, jiù kāishǐ gōngzuò.
他一到家,就开始工作。
As soon as he gets home, he starts working.
Yī gè píngguǒ dōu hěn hǎochī.
一个苹果都很好吃。
Every apple is delicious.
Tā zhǐ xūyào yī liàng chē.
他只需要一辆车。
He only needs one car.
Tā yī tiān chī sān gè píngguǒ.
她一天吃三个苹果。
She eats three apples a day.