昨天 zuótiān
今天 jīntiān
明天 míngtiān

昨天 Pronounced like “z-whoa t-yen”
今天 Pronounced like “jean t-yen”
明天 Pronounced like “meeng t-yen”

昨天 means yesterday
今天 means today
明 means bright, clear
明天 means tomorrow

When using time words such as 昨天 or 今天, the time word always precedes the verb. This allows for some customization when forming a sentence.

昨天我吃七个饺子。
Zuótiān wǒ chī qī gè jiǎozi.
Yesterday I ate seven dumplings.

我昨天吃七个饺子。
Wǒ zuótiān chī qī gè jiǎozi.
Yesterday I ate seven dumplings.

The sentence structure now changes to either:

Subject + Time + Verb + Object
or
Time + Subject + Verb + Object