This is a tutorial that shows how to use Mesh. Press the right and left arrows for the next step or the previous step.
NOTE: You no longer need BYOB (Build Your Own Blocks) to use Mesh. MathWizz has a tutorial that shows how to hack Scratch 1.4 and unlock Mesh. It is also likely that Mesh will be availible in Scratch 2.0. You can see MathWizz's tutorial here: http://scratch.mit.edu/projects/MathWizz/849173