What is a good website to learn using active directory?

The BEst and most reliable website is of Microsoft, you will get everything of AD

http://technet.microsoft.com/en-us/library/bb726976.aspx

this is one of popular site to learn AD after you finish the fundamental and you start work in it.
http://stackoverflow.com/questions/663402/what-are-the-differences-between-ldap-and-active-directory

you can learn and get deep knowledge about AD and windows server from below link :

http://technet.microsoft.com/en-us/library/bb727169.aspx

 

Regards,

Amir Imtiaz