In the Philippines, if you are employed, your company will compute for your form 2316. You will just have to sign it and they will take care of the filing. Your tax refund or payable will be computed in you December salary and will be added or subtracted depending on the tax withheld.
Here, they employ the "honesty" system and every individual has to file their returns. Employees would received their T4 from their employees and need to transfer the amounts in the correct line in the tax forms. This is were it gets tricky. You may not be able to subtract anything from your income, but there are a lot of tax credits like donations, public transit, tuition fee, books and trades tools available at your disposal. Just be aware of it because every year Canada Revenue Agency will implement new laws and amounts.
If you belong to the low income families, you may also be eligible for some benefits like Working Income Tax Benefit, HST/GST credit or in our case, Ontario Trillium benefit.
Anyway, just a last minute advise, file early so that your refund will arrive early. =)