忘 + 了 + Verb Phrase / 忘 + Object
忘 (wàng) means "to forget" and is used when someone fails to remember to do something or loses a memory. It is often followed by 了 (le) and can take a verb phrase as its object to indicate what was forgotten.
我忘了带钥匙,进不了家门。
Wǒ wàng le dài yàoshi, jìn bù liǎo jiā mén.
I forgot to bring my keys and can't get into the house.
对不起,我忘了今天是你的生日。
Duìbuqǐ, wǒ wàng le jīntiān shì nǐ de shēngrì.
I'm sorry, I forgot today is your birthday.
他出门太急,忘了关灯。
Tā chūmén tài jí, wàng le guān dēng.
He left in such a rush that he forgot to turn off the lights.