I'm still new to Minecraft and I tried to make a multiplayer server to play with my friend, but there is something I don't understand, Server Address? Can someone explain what that is?
If you're wondering about something more specific, take a look at the article on the server.properties file, which explains how you can customize your server to fit your needs.
As for what exactly
server-ip does, it's unnecessary. You might as well leave it blank.