I am trying to download Single Player Commands for minecraft. I download the folder and I followed the instructions until this instruction came up:
Open the jar file (using an archive utility, such as 7zip) in the mod directory you created (eg: 1.6.2.jar) and copy all of the files into it except for WorldEdit.jar
I tried to open the Java Jar file but the message, 'File cannot be opened, check the console' came up. Please help, I really really want to get single player commands.
I am a Mac user, and I have Mountain Lion.
Here is the link to where I got the Single Player Commands file and the instructions to get it.

Check Solution