The local machine most likely does not have a public ip address.
When you turn on file sharing in FM a ip address will show. if you get a number like 192.168.#.# , 10.#.#.# , 172.#.#.# then it has a private ip address and you will need to set up port forwarding in router. Note it is best to make the ip address static on the computer so it does not change when your computer reboots.
Access your router setting then click on port forwarding, add new, then type port 5003, then type the ip address that is shown on your computer (hosting computer). Example 192.168.1.2
Go to a website such as www.ipchicken.com, this is your modems pubic ip address which is the ip address you use from outside of your local network. Note the ip address may also change on your modem unless it is static. The public ip address will be assigned by your internet service provider, so if you need static you will need to call your ISP.
Open port 5003 on your firewall.
In the Start (or lower left Windows menu) search box type cmd to bring up the command prompt and type ipconfig and enter. ipconfig /all will provide more info