The taxes will come out of that $40 dollars, as to how that will occur, you will need to look at your paystub.
Your employer should be taking the taxes off, but if they are not OR if they are taxing you incorrectly, when you file your taxes at the end of the year you could owe Canada Revenue Agency (CRA) money. If your employer is not taking off taxes, that will be reflected on both your paystub and the T4 they will give you at tax time. If they are not taking off tax, it will be up to you to deduct it from yourself and pay your taxes at the end of the year.

Once you file your taxes, you will receive a Notice of Assessment from CRA stating either:
1. You owe them money
2. They owe you money
3. The correct amount of taxes were paid and no one owes anyone

Taxes in Canada are based on yearly income, so if you worked at company A and made $70/h then moved to company B and are making less, you could have some problems. Company B is basing your taxes based on what they are paying you, and not taking into account how much you have already made.
Check your paystub to verify if indeed taxes are coming off.

Also, remember you will have more deductions than just tax, you will also be paying into Employment Insurance (EI) and Canada Pension Plan (CPP).