Scratch is one of the best programs for beginner designers and I am sorry for all the people who use more advanced programs than Scratch, but this instructable is for everyone and anyone.
The thing that most people don't understand about games is that it takes loads of time to create one. If you refer back to one of the first Mario games, and look at one level, it could take you between one and three days to design something that works as well as that IF you can program decently. For this reason I have created a one level Super Mario game which has almost all the 'rules' of how to make your game work.
During this instructable I will be referring to certain things and will just call them by either abbreviations or by other names entirely. As to not confuse you I have created a list of what I call what:
Rules: The things on the left side that you can pull onto sprites script
(go to) Paint: When you go to costumes of a sprite and click edit, it will bring up the Paint page
S(x): Sprite number x
g+w colour: the colour in Paint that is the bottom right colour, the one with 4 blocks in it.