邮局 (yóujú) is a noun meaning "post office." It refers to the physical office or organization responsible for mail delivery and postal services. It is a common everyday word used when discussing sending or receiving mail and packages.
我要去邮局寄一个包裹给我妈妈。
Wǒ yào qù yóujú jì yī gè bāoguǒ gěi wǒ māma.
I need to go to the post office to mail a package to my mom.
这附近有没有邮局?我需要买邮票。
Zhè fùjìn yǒu méiyǒu yóujú? Wǒ xūyào mǎi yóupiào.
Is there a post office nearby? I need to buy stamps.
邮局下午五点就关门了,你得快点去。
Yóujú xiàwǔ wǔ diǎn jiù guānmén le, nǐ děi kuài diǎn qù.
The post office closes at five in the afternoon; you'd better hurry.