Just want to get your feet wet? Try the hour of code!
Learn to Code with Processing
Serious about learning how to program? Go through these in order:
Use mouse and keyboard input to make interactive sketches.
Use patterns to repeat work without repeating code.
Create variables that hold multiple values.
Create an object that stores other objects.
Display and manipulate image files.
Use libraries to expand what Processing can do.
Advanced Processing Tutorials
Read through these as you need them!