This questions and many others for a beginner are answred in many apps notes from different manufacturers.
Suggest you visit www.powerint.com and www.ti.com and look for seminars and app. notes on the subjet. Guess it will help U better as there U will find complete info.
Current Mode vs. Voltage Mode,Which mode is better?
It depends on ur system application. u may visit National,Ti and Onsemi website and will find many application note.