How do I find out how much tax I have to pay?
To work out how much tax you pay on your taxable income, you have to complete Schedule 1 for your federal tax and the ON428 for your Ontario tax.

What is a non-refundable tax credit?
The government allows you to claim certain credits which help to reduce the amount of tax you have to pay. These tax credits are non-refundable. You can use these credits to reduce to zero the amount of tax you have to pay. However, if your tax credits are bigger than the tax you had to pay, that's just too bad. You can't keep them for next year. If you have $1200 of federal and provincial non-refundable tax credits and have to pay $1000 of income tax, the non-refundable credits will reduce your tax to zero, but the extra $200 worth of credits disappears. This amount can't be carried over or refunded to you..

What sort of things can I claim to get these tax credits?
Everyone can claim a basic personal amount. If you are married or have a common law partner, you may be able to claim an allowance for that person. If you have an eligible dependant, you may be able to claim an amount for this. If you have medical expenses, you may be able to claim an amount for this. When you have worked out how much all these amounts come to, then you have to add them all together. Next, you have to find what 16% of the total is. (The percentage may change from year to year.) This is what you can claim as a federal non-refundable tax credit.