The format should clearly list out your roles and responsibilities, period of work, no. of hours worked per week, designation, annual salary and benefits and should be signed by relevant person in your organization. It should also contain contact details of your organization.
Reference letter will be in a similar format and must be obtained from your current and all previous organizations for the last 10 years.
You may also check Documentation checklist for PR available at
http://www.cic.gc.ca for a clearer understanding.
