How to make a multiplayer server in Minecraft SP?

In my mac's minecraft, I've always wanted to play Minecraft Multiplayer with the free one (Minecraft SP). I read that a lot of people said you can't, however my friend's cousin was able to make one from the free version (Minecraft SP). Can anyone tell me how? Please explain if so.

Added (1). thanks to those that have answered, but I forgot to mention that I would much prefer LAN, but Online is still ok…

Added (2). thanks to those that have answered, but I forgot to mention that I would much prefer LAN, but Online is still ok…