When does its have an apostraphe?

An apostrophe is used when you want the Word to mean "Belongs to".

Examples: "I have two Freds in my family." These Freds are not being used in the sentence in the sense that they belong to anyone, so no apostrophe is used.

"Yesterday was Fred's birthday." The birthday is something that belongs to Fred, so an apostrophe is used.

An apostrophe is alos used if the Word is a contraction. That is when a Word is shortened. Examples: 'Do not' is shortened to don't. 'Will not' is shortened to won't.

'You are' is shortened to you're. 'It wil'l is shortened to it'll, 'Shall not' is shortened to sha'nt, and so on.