I've seen confusing instructions for Single Player Commands in Minecraft. How do I install it?
Edit: SPC for 1.8 is now out!
However, once it does become available, this is how you install it:
Or, you could use the automated installer
Single Player Commands can be installed with the automated installer that is available from the link on their thread. Running this file will allow you to patch your Minecraft.jar file with the SPC mod. You can back up your maps and/or binary before doing so, in case you wish to revert later.
After installing, launch Minecraft then you can use any of the listed commands by pressing T or the chat button, typing them in and hitting enter.