Coinsurance is the percentage of the service you are responsible for. For example, 20% coinsurance means you pay 20% of the bill and your insurance carrier covers the rest. 

If it says 20% coinsurance after deductible, that means you will pay the full cost of the service until the deductible is met, then you’re only responsible for 20%.

Once you reach your out-of-pocket max, your plan will pay at 100%