How do I get my "localhost" to work? (OS X Version 10.8.3)

OS X Version 10.8.3, How do I get my localhost to work?

nancys-imac:~ bacck$ cd /etc/apache2/users

nancys-imac:users bacck$ sudo pico back.conf

Password:

<Directory "/Users/bacck/Sites">

Options Indexes MultiVews

AllowOverride All

Order allow,deny

Allow from all

</Directory>

(Note: Once I confirmed that I've typed everything correctly, I press: Control and key "X" to exit pico

Type in "Y" for YES and then "RETURN" to confirm the file name)

BEFORE ALL THIS...................................................................

localhost: response "It works", before I made up a personnal subfolder: name "Sites", which is in my Home folder "back".

BACK TO TERMINAL............................................................

nancys-imac:users bacck$ ls

Guest.conf bacck.conf bacck.conf.save

and localhost is not working!

HELP :~