NAT enables private IP networks to connect to the public Internet by allowing private IP addresses to be translated to public IP addresses. There are three main types of NAT: static NAT maps individual private IPs to public IPs manually; dynamic NAT maps private IPs to public IPs automatically from address pools; and PAT maps multiple private IPs and ports to a single public IP and port numbers to distinguish connections. NAT allows private addressing in local networks while also connecting to the public Internet using public IP addresses.