It's is a contraction for it is or it has.

Examples:

It's = It is

"It's my bedtime."

"It's time to go."

"It's only 11 o'clock."

"It's over there."

It's = It has (not possessive)

"It's been a long time."

"It's been brewing awhile."

"It's got to happen soon."

Its indicates possessive.

Or, put a more technical way, its is the possessive form of the neuter pronoun "it" — his, her, its.

Examples:

Its possessive

"Every dog has its day."

"The jury has reached its decision."

"Stop its momentum!"

"Guess its color."

A Good Rule of Thumb:

If you can replace it with his or her, there's no apostrophe.

You're is the contraction of "you are" and is often followed by the present participle (verb form ending in -ing).

You're going to be late.

Is that what you're wearing?

I think you're lying.

If you're ready, we can go.

I can't believe you're a doctor!

When you're my age, you'll understand.

The Bottom Line

The confusion between your and you're occurs because the two words are pronounced pretty much the same.

The ironclad rule - no exceptions - is that if you're able to replace the word with "you are," you're saying you're. Otherwise, your only choice is your.