How do I know if I have a cracked heater core? And how do I replace it if so? on 2002 Mitsubishi Montero Sport

I was told by a friend I have a cracked heater core, I don't know! I have what looks like steam or smoke & the smell of the radiator coming thru the vents on the interior. Also I have what looks like corrosion & rust in the radiator reservoir.

Asked by for the 2002 Mitsubishi Montero Sport
Having the cooling system pressurized with a tool that looks like a bicycle pump that has a pressure gauge attached will help locate the leak but it sounds likely the heater core is leaking from your description and it will burst and send hot coolant into the interior of your car if it fails. It's about a 4.5 hour job to replace.