Press the green flag, and watch! Press the arrow keys for demonstrations. If you can't be screwed watching the whole thing, and just want to get the script (most of you guys ;D), see inside. For those of you who say it doesn't work, it does, just change the terrain colour to the colour I used, or change the various "touching colour [ ]" blocks to the colour of your choice.
WOAH 2500+ LOVES If you are having problems, instead of saying "I glitched through the wall" or whatnot, say "I glitched through the wall" and then put a link to your project. The platforming script I use is a mixture of many that I have seen in other projects. I have edited them and perfected them (in my eyes, at least). I would rather you give credit if you use this, but I don't really mind if you don't. For a tutorial on smooth velocity, go here: http://scratch.mit.edu/projects/30980702/