Just press the green flag and wait a few seconds for it to connect and update. Test it by running the project in multiple tabs. If possible make sure you are alone in your own channel. The game should allocate you a channel automatically. If it doesn't then just hit the flag again. You must be a fully-fledged Scratcher to be able to access cloud variables. The maximum number of people is 5. If necessary I can increase this limit.
Anyone can use this in their projects by saving the main sprite and copying it to your project! You will need to refill some lists. The project contains a useful string to int encoder and decoder at the bottom of the main sprite. You will need to fill the 'letters' list with all lowercase letters and numbers.