Its or It’s

Use its as the possessive of (or belonging to) it.

The doggie wags its tail.
Its color is brown.

Even though possessives of nouns (dog’s tail, man’s hat) have the apostrophe, its (as belonging to a thing or animal) one does not.

It’s is the contraction for it is and has an apostrophe.

It’s cold outside. is the same as It is cold outside.
Now it’s raining.  is the same as Now it is raining.