昨天 (zuótiān)

昨天 means yesterday, the day before today. It is placed at the beginning of a sentence or before the verb as a time expression.

Meanings

昨天我去了图书馆。 Zuótiān wǒ qù le túshūguǎn. Yesterday I went to the library.

她昨天没有来上课。 Tā zuótiān méiyǒu lái shàngkè. She did not come to class yesterday.

你昨天晚上做什么了？ Nǐ zuótiān wǎnshang zuò shénme le? What did you do last night?

昨天的考试很难。 Zuótiān de kǎoshì hěn nán. Yesterday's exam was very difficult.

昨 contains the character for "work/make" on the left and a time radical. Think of it as the day you already "made" your effort, now passed.