Port forwarding allows one computer on a network to connect to another computer on another network.
If you want someone to connect to your computer from theirs in order to access your programs and files, you could use an application like MS Windows remote desktop connection.
Through remote desktop connection, the other person would send a request to your public IP address to access port number 3389 (the default port for remote access). In order for your router to forward your request there, you must configure your router to do it.
NOTE: An IP address is like the phone number for a company, and the port number is like the extension to a certain department within the company.
To find your router's IP address, you must open a command prompt in Windows, type "ipconfig," and hit enter. Here, you will see your IPv4/v6 address, subnet mask, and default gateway. You'll need the IPv4/v6 address and default gateway IP addresses to configure your router.
Depending on which router you use, the configuration page might look a little different. In any case, you'll access your router's configuration page by typing its IPv4/v6 address into a web browser, going to the port forwarding section of the page, and entering a name for your application such as "Remote Desktop." Then, you enter the port number (entered into the internal and external fields) and the default gateway address of your computer into the corresponding fields. Finally, you will "enable" port forwarding.
Now, when the other person sends a request to connect through port 3389, your computer knows where to forward the request.