By setting up a Minecraft server, you can essentially create your own version of the game with unique rules and an exclusive community of your choosing. Once you are in control of one of these ...

exec java -Xmx1G -Xms1G -jar minecraft_server.jar Allocate as much memory as you’d like by changing ‘1G’ to the number of gigabytes you’d like to set aside (2G for 2GB, 4G for 4GB, and so on).

So, if your IP address is 48.32.34.102, and your Minecraft server is on port 25565, then you'd tell your friends to enter 48.32.34.102:25565 in the address field of Minecraft.