as mentioned by BC2013 the validity of the Visa stamped is for one year from the date of Medicals or the validity of the Passport. This is the time in which you and your dependents have to land in Canada, after you have done first landing then to maintain the PR status you need to stay in Canada for more than 730 Days (2 Years) in every rolling 5 years.
To get the Citizenship you need to stay for 3 years in a period of 4 years and you can apply for Citizenship and that will remove the condition to maintain the PR.