BitLocker Drive Encryption explained:

Bitlocker drive encryption is a security feature available on ultimate and enterprise edition of window vista and window 7 as well as  Windows Server 2008 and  Windows Server 2008 R2. It is designed to protect the data of entire volume by the encryption, by default it use the AES algorithm encryption with 128 bit key.It is the very good security feature my microsoft...Lets start with Bitlocker:

1.how to enable bitlocker:

(a) go to control panel and open BitLocker Drive Encryption

 

(b) open BitLocker Drive Encryption:

(c) click on turn on bitlocker it'll ask you for password :

 

 
 (d)  click next it'll ask you to save the recovery key save it wherever you wish:

 
(e) after that click on start encrypting:

 
After encryption completed it'll ask you for password that you have given in case u forgot the password you can't retrieve your data also so it is very much necessary that keep your recovery key safe which is only way to retrieve your data