Windows has a built-in service called Remote Desktop, which connects two computers over a network. Once connected, you'll see the remote computer's desktop as if you were sitting right in front of it, and have access to all its programs and files. These instructions describe how to configure the remote computer settings to allow a connection from another location, such as your home. It also covers how to make the connection from home, using VPN and the IP address of the host PC.
Steps 1-5 pertain to your office computer. The remaining steps are for your Mac.