How do i tell if the heads creaked on a 91 celica

A cracked head or blown head gasket,will cause your vehicle to have a miss in the cylander where the crack is or where the gasket is blown. you can also see coolant leaking if the gasket is blown. you can also see water in the oil,and white smoke come from the exhaust.
to tell for sure that the head is cracked,and not just a blown gasket is to remove the head. you will instantly see if the gasket is blown. if its not,then turn the head upside down and look at the small space between the valves,as this is where 99% of cracks occur.

Get a compression tester and check the compression of each cylinder this will tell you for sure you dont need to remove the cylinder head unless you are going to repair the gasket.