Its vs. It's

A). Its is a possessive determiner. (Possessive Pronoun)

Meaning: belonging to or associated with a thing previously mentioned or easily identified.

e.g. Turn the camera on its side.

B). It's is the short form for either it is or it has. (Contraction)

e.g. 1). It's my fault.  2). It's been a hot day.

If you have trouble keeping them straight, try remembering this phrase:

Use its like his; use it's like he's.

1). His tact impressed us. -> He's tactful.
2). Its beauty pleased us. -> It's beautiful.