The first one is to knit the collar, or use a provisional CO and knit only a few rows, and then shaping the neckline with short rows starting from the front and working towards the back:
(Pictured from above: the white oval circle in the middle is the neckline and the dotted lines are imaginary raglan seams.)
The second one is to shape the neckline starting from the back and working towards the front:
This is the one I use most, since it’s easier to use with a pattern.
The same principal goes also for cardigans, but instead of knitting in the round, you knit back and forth: