You begin with the stitches around the neck and 4 markers are placed to show where the front, the back and 2 sleeves are. Where the sections meet is the increase raglan lines are.
If you want the back higher, only cast on enough sts for the back and 2 sleeves and 1 for each of the fronts. Knit a few rows flat, doing increases at the markers on every RS row as well as an inc at the beginning and end of the row. After a couple of inches, then Cast on stitches at the end of a RS row and join it to the sts at the other front for the front neck. At that point you should have the same number of stitches on the front as for the back. Here's a tutorial
that shows the method I described which is probably not the same as your pattern.