What are the stuff to learn to become good at Kernel,drivers?

C and Assembly( your gonna need the asm / microprocessor internals knowledge). Also I'd recommend minix as a start http://www.minix3.org/, here's a really basic intro to drivers to give you the basic idea what that entails, http://www.freesoftwaremagazine.com/articles/drivers_linux.

One thing, if you're just starting out (which it sounds like), I would NOT recommend looking at the linux kernel src. And lastly, modern operating systems by tanenbaum is a good introductory text that has the plus of being a fun read. Good luck!

Learn C.

Study the high-level kernel architecture of the OS you're interested in.

Browse interesting kernel code.

For Linux, read anything Greg Kroah-Hartman puts out. Attend any kernel driver classes he gives.

The O'Reilly kernel Linux drivers book is probably still being updated, also.

For the Windows kernel, the latest edition of the Microsoft Press "Inside Windows" is gold.

For the OS X kernel, about your only resource is developer.apple.com

http://www.kroah.com/log/

http://www.kroah.com/linux/