I've tried for hours, but each time i try, i can't get SingleplayerCommand mod on minecraft?

I've followed all of the directions on the minecraft forum. They are 1.6.2 directions, and i'm using them for 1.7.4.

1.7 update for Minecraft changed the way mods work, and how they function, therefore no mods from previous versions will work in 1.7.4. So, the Single Player Commands won't work with the version.

What I suggest is moving your Minecraft to 1.6.2 then installing it to work, or use a different mod with 1.7.4. Sadly, the mod isn't updated yet but might be in the future.