Could anybody explain nat and nat overload(pat) setup for configure a webserver connection to the outside network?

If this question is anything but academic, let someone familiar with the network securely configure the webserver access, otherwise your webserver will likely be compromised quickly.

With NAT, one or more internal addresses are mapped to one or more external addresses, either statically or dynamically.

With NAT overload, multiple addresses or ports are usually mapped to a single address or port.

For the most basic webserver, ports 80 (HTTP) and 443 (HTTPS) and a single external address are NAT'd to a single internal or DMZ address at ports 80 and 443 or custom port numbers. Other ports, such as 22 (SSH), to facilitate remote maintenance or backup of the server could also be configured.