You've probably heard the phrase 'nothing is free' many times in your life. Usually when you see the word free there are strings attached. Be it a buy one get one free deal at the local grocery store, free water heater, or sugar-free beverages stockpiled in your fridge. The word free is freely used and not always as advertised.
One area where the word free is used and actually means what it says is in regards to your health and OHIP. OHIP is the Ontario Health Insurance Plan that covers many medical expenses and is available to any Canadian citizen who lives in Ontario for at least 153 days during a 12 month period and live in the province at least 153 days out of their first 183 days after becoming an Ontario resident and has made Ontario their primary residence.
Those are the basic requirements in order for you to be eligible for medical expenses covered under OHIP. OHIP's focus is on medicine so the dentist you go to is not covered.
Understanding OHIP isn't all that hard really. The Canadian government provides Canadian citizens with a wide range of medical coverage and health treatments free of charge. Each province has their own health plan that ensures you get the services you need.
Not everything is covered but for the most part any medical expense you need covered, be it surgery or x-rays, is paid for by the government. Canada's health plan coverage is one of the many attractive features it provides its citizens. You always hear about Americans complaining about HMO prices but you never get that from Canadians because of how awesome the health plan is here.
Medical coverage is usually provided for anything that is necessary such as an appendectomy but won't cover procedures not needed such as cosmetic surgery or teeth whitening. For instance if you want to get some rhinoplasty done the government won't cover the procedure if it's for cosmetic purposes only but will perhaps cover part of the costs if it's done to fix a breathing problem.
Coverage for certain procedures depends on if it's necessary for your health. OHIP will cover something like hyperbaric therapy if it's an emergency situation and prescribed by a doctor.
If you aren't sure if something is or isn't covered by OHIP such as chiropractor visits or certain pain medication you should contact your local OHIP office and ask.