How important is registry and what are basic editing done on it?

The Windows registry is a database used to store settings and options for all current version of Microsoft Windows. It contains information and settings for all of the PC's hardware, software, users, and preferences. Whenever a user makes changes to the control panel settings, file associations, system policies, or installed software, the changes are reflected and stored in the registry. 1,000 registry tweaks and a tutorial may be found here:
Windows Registry Guide - Free software downloads and software reviews - CNET Download.com

Another source to check:

Windows Registry Guide - Registry tweaks and fixes for Windows systems

Hope this helps.

I would suggest to use a system utility tool to fix registry errors. I would recommend to use SpeedUpMyPC 2012 to fix registry errors and optimize PC to its best performance.