The basic principal is called 'VHost' or 'Virtual Hosts'. A VHost config will look something like
<VirtualHost *:80/>
ServerAdmin you@domain.com
DocumentRoot /var/www/html/yoursite
ServerName yoursite.com
ServerAlias www.yoursite.com
</VirtualHost>
<VirtualHost *:80/>
ServerAdmin you@domain.com
DocumentRoot /var/www/html/yourothersite
ServerName yourothersite.com
ServerAlias www.yourothersite.com
</VirtualHost>
For a more in-depth example just google 'Apache Virtual Hosts'
You might also want to look into CPanel, Plesk, Webmin and similar GUI based config generators to look after everything on your server