This is the official government page and is often the first place people visit when they start to think about immigrating to Canada. The website contains detailed and accurate information on how to apply for immigration, what to do after you arrive, how to sponsor your family for immigrating to Canada, how to apply for refugee status and as well as procedures for applying for Citizenship.
I would highly recommend you check this place first and also double check the information you obtain from other places again here to make sure they're correct.
