The pattern includes a diagram that shows which direction each entrelac square should be knitted, and an explanation of how to make a square or triangle in that direction. It is possible to teach yourself entrelac from the directions.

From the pattern description:
The technique used in the Rainbow sweater is referred to as diagonal patchwork (entrelac) knitting (see p. 31 and p. 134). Rainbow has, as it were, two fronts, to be used according to taste and wish. Consequently, the neckline shaping is identical on both sides.
The texture of the knitting should be firm, which sets off the technique more clearly and attractively. In the instrucitons I have not indicated the exact distribution of the colors, since I prefer to leave it to your imagination.
Knitting with as many shades of color as in this sweater results in a great number of loose ends to be fastened, but it should not be too much of a burden, especially if done continuously. It is, in fact, possible to fasten the yarn automatically at one end by picking up stitches with double (folded) yarn.
The bottom (i.e., around the hips), neckline and wrist edges are picked up and knitted at the end. In order to make them match the colors of the sweater, you may want to knit them in several overlapping parts (see the photo on the facing page).