very simply : INTARSIA « Tin Can Knits
Intarsia Knitting, Tute, Part 1. By k1p1 TV. Exceptionally clear video, focusing on the all-important INTERLOCK technique. (Listen w/ headphones, as the volume is too low.) The clarity of the images makes this tute worthwhile.
Intarsia: straight lines instead of jagged edges http://www.knittingdaily.com/articles/knitting-techniques/colorwork/smooth-the-jagged-edge-with-shaped-intarsia/
Intarsia knitting (how to)
Neater intarsia - A simple fix for uneven stitches around a vertical color change. From yarnsub.com blog
Intarsia What is it & how to use it
knitting: very detailed and helpful tutorial on how to knit intarsia. very cool!
Introduction to intarsia knitting - from Twist Collective
Brilliant. The intarsia box (long needle or straw as a spindle, held on point end with a point protecter) keeps your many little balls of yarn in a neat line while you work. Much more portable, too!