Hello!! follow these steps to see if your issue is resolved.
1- Open CMD and place ipconfig /all and select the IP either Wi-Fi or wired. (that you are going to place it in the server properties file )
2- You must open port 25565 TCP with the IP associated with your machine. ( the same one you put in server properties )
3- you must give your friends the public IP. you can find it at whoismyip.com