Can something change states of matter how do you know

Yes, it can change states of matter from heat. Like ice, ice changes it's state of matter from the temperature it is in, which causes it to turn into a liquid. (another form of matter) Again with heat, if water is boiled to a certain temperature it converts to a gas. Now with cold. If water is at such a coke temperature it will turn to ice, a form of matter. Now when a gas is cooled down, the atoms comprising the gas have less energy to move around.