Permanent residency status in Canada is granted as a result of the Immigration Visa, a type of visa issued to approved immigrants. Typically an immigrant visa is valid for several months and must be used within this time or it will become invalid, requiring a new application for immigration. After you have an Immigrant Visa, you will be issued permanent residency in Canada once you arrive at the airport or land border in Canada and have the visa processed there. When you arrive at the airport or land border, the customs agents will refer you to an immigration officer who will verify the information on the immigrant visa, then sign and approve it.
After receiving permanent residency status, you will need proof of your permanent residency to show to airlines when you travel, or to Canadian customs when you come back. If you plan to leave Canada, you should obtain a Permanent Residency (PR) Card. The PR card does not impart permanent residence, but it is proof that the holder is a permanent resident. Within Canada it is also a useful form of identification that can be used to obtain other necessary documents such as a Social Insurance Number or a Health Card. Normally, after an immigrant visa is processed at the airport or border, the PR cards will be mailed out to the new immigrant within a couple of weeks.
The PR cards are valid for 5 years and may be renewed repeatedly and indefinitely. In order to be able to renew the card, and with certain exceptions, the holder must show that they meet the residency requirement of living in Canada for at least 2 of the past 5 years. This means that a new immigrant can leave Canada for up to 3 years within the validity of their card, and still maintain their residency. How the immigrant chooses to divide this up is entirely up to them. An immigrant could arrive in Canada, get landed, then leave the next day and not come back for three years. However, most people prefer to leave the country only when necessary in order to qualify for citizenship as soon as possible. To obtain citizenship, a permanent resident must be physically present in Canada for at least 4 of the 6 years before applying.