its / it's

its: possessive determiner similar to 'my' or 'your'

its：物主代词，和“我的”或者“你的”是一类的。

Examples:

例句：

Its color is red.

The dog didn't eat all of its food.

它的颜色是红色。

这只狗没有把它所有的事物吃掉。

it's: Short form of 'it is' or 'it has'

it's：it's是it is或者it has的缩写。

Examples:

例句：

(it is) It's difficult to understand him.

(it has) It's been a long time since I had a beer.

（it is）要理解他太困难了。

（it has）我很久没喝过啤酒了。