Things to remember:
* Actually you don't have to create a new world. Commands can be added to existing worlds by clicking on the "pencil" to the right of the world's name, changing the Difficulty to Hard, and then the "Cheats" option will show up. However....
* Read the warning carefully! Once cheats are enabled, Achievements are disabled for that world forever!
* Not all "commands" from the PC are available, but the most used ones are. Actually a new world window pops up after hitting "t" (not sure what you hit on touch screens), then put in a "/" and a "guide" shows up showing you what's available, the correct spelling, and proper formatting. Sorry, for now you can't just "choose" from the list- you actually have to type the command in.