In your offer letter, it should state the following:

- basic salary
- housing allowance (or accommodation allowance)
- transportation/petrol allowance (or a company car provided)
- education allowance for your kids (if any/applicable)
- return ticket after completion of X number of months (1 or 2 years)
- Number of leave days per annum (which is at least 21 days per every year of service).

The above details are also stated in your contract of emp0loyment which would be (in English and Arabic) in triplicate copies(1 for the labour Office, one for the employer and 1 for you)

The CoE is part of the documents submitted to the Immigration in acquiring your working visa.

hope you find the above info helpful.

You could also check the hukoomi website for more info: http://portal.www.gov.qa/wps/portal/homepage