The www folder is created by most distributions during the apache setup process. As the setup process is run by root, the www folder is owned by root. Use
ls -al in
/var to look at it's permissions.
drwxr-xr-x 5 root root 4096 May 2 11:34 www
chown are GNU coreutils that you can use to modify the permissions of unix directories.
chown to change the owner and group of
/var/www/html/ to your user and group, e.g.
sudo chown -R jason:jason /var/www/html/
As you're likely to start putting PHP scripts in here, you'll then need to use
chmod to make sure the apache user (in most cases
www-data) is allowed to execute them.
Try and understand how Unix permissions work before proceeding any further as it will save you some time down the line. Good luck.