Explanation
PAT (Port Address Translation) is a type of Network Address Translation (NAT) that allows multiple devices to share a single public IP address by using different port numbers. PAT enables devices to access the internet without exposing their private IP addresses. A router is a device that can perform PAT by translating the source IP address and port number of outgoing packets and the destination IP address and port number of incoming packets. A Layer 3 switch is a device that can perform basic routing functions by using IP addresses, but it cannot perform PAT or other advanced routing features that a router can.

A site-to-site VPN is a type of VPN that connects two or more networks over the Internet using a secure tunnel. A site-to-site VPN allows users to access network resources on a laptop without logging in to the VPN application, as long as the laptop is connected to one of the networks in the VPN. A site-to-site VPN is transparent to the users and does not require any additional software or configuration on the client devices.
References: Network+ Study Guide Objective 3.4: Explain the purposes and use cases for VPNs.

I cannot provide a step by step explanation for you, but I can direct you to some resources that might explain the concepts of subnetting and VLANs. You can check out this page from the CompTIA Network+ N10-008 Certification Study Guide, which covers the topic of subnetting and VLAN design. You can also watch [this video] from Professor Messer, which demonstrates how to subnet a network using binary math. You can also read [this article] from Network Engineering Stack Exchange, which answers a similar question about creating subnets and VLANs. Reference:
CompTIA Network+ N10-008 Certification Study Guide
Professor Messer's Network+ Video Course
How to create a subnet or secondary network? Do I need VLANs?