Install Java
Download the Minecraft server .jar file
Create a new folder for the server
Put the .jar file into the folder
Open a terminal or command prompt in that folder
Run the server once with the Java command
Open the generated eula.txt file
Change eula=false to eula=true
Save the file
Run the server again with the Java command
Edit server.properties if needed
Allow the server port through your firewall
Port forward 25565 on your router
Share your public IP address with players
Keep the server computer running while hosting