GCMS stands for 'Global Case Management System' and is adopted by CIC as a new computer system to maintain case history.GCMS notes are essentially all of the notes that CIC will have on your file (Including Visa officer notes)
There are a bunch of companies that offer services where you can order the notes from them at costs around $40 - yet it only costs either Free or $5 to get them from the governement (depending on the service you want)....
If you're currently residing in canada you can order them yourself for or you can have a friends/family member order them for you.
Go through the various options in the form and choose things that relate to immigration.
The notes will also tell you if you have passed the most important parts of the application i.e. Medical, background, security and eligiblity. You can order by visiting the below website.
http://www.cic.gc.ca/english/department/atip/requests-atip.asp