I am using AVr studio 4.19 & winavr gcc.

1. Where I can find examples codes for learning.
Someone here pointed http://winavr.scienceprog.com/avr-gcc-tutorial?page=1
but it contains few examples & not very well aligned.

Anyone knows better source

 

I suggest you get the latest atmel studio, the the code completion and suggestions make life much much easier.

Did you read the complete datasheet? There are quite a lot of examples for the beasic control of how to use all the peripherals. I think there are also some examples at http://www.nongnu.org/avr-libc/user-manual/index.html
Otherwise it is usually good to google for the specific part that you need help with.