1) Your employer is taking the taxes off your paycheque and forwarding that to the government. (15.5% fed, 10% alb... assuming less than $37,178). This way you won't be burdened with a huge tax bill at the end.
2) you're paying into the CPP (Canadian Pension Plan) and Employment Insurance. You don't get any back of it back at the end of the year.
At tax time, you can file for tax credits (school, textbooks, medical, disability, etc.)
"Science without religion is lame, religion without science is blind." - Albert Einstein