Dear Arvindji , Gurfateh.
As we were told in the 'santhya' (learning Gurbani) , there are three pothies out of Guru Granth Sahib 1) Panj Granthi 2) Bhagat Bani 3) 22 Vara.N.Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/history-of-sikhism/451-punj-granthi.html
1) Panj Granthi contained Five Banies i) Bavan Akhri M-5 ii) Sukhmani Sahib M-5 iii) Anand Sahib M-3 iv) Onkar M-1 and v) Sidh Gosti M-1
Later the Printer/publishers added the Nitnem and other banies in it.
2) Pothi Bhagat Bani- contains the bani of Bhagats and Bhatts. Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=451
3) Pothi Baee Vara.N (22 vars) as the name shows contains all 22 vars from Guru Granth Sahib ji.
We were told that if a sikh does not study the whole Gurbani with meanings , he should ,at least study these three pothies with meanings and read these banies at his home whenever he finds time. out of them, being easy to read, Sukhmani Sahib is popular and other banies are known least.