You need root permissions to write to /var/www folder. You can create/edit files in /var/www folder with sudo.
sudo gedit /var/www/myfile.html
sudo touch /var/www/myfile.html # only to create a file.
You can choose one of your own directory as your web folder. You can create a folder in your /home directory and change the web server's folder to it.
you can replace "/var/www" string in following files into your own directory path and then you can use new directory as your www folder.
After changing contents of the above files, run
sudo /etc/init.d/apache2 restart
to restart webserver. Then you will be able to use new directory as the web folder.