They're knit in one piece from the top down, similar to a raglan, or 'half' a raglan. You begin with something like 7 sts say - 2 edge sts, 1 for the first section, 1 for the center st, 1 for the 2nd section and 2 edge sts. Each RS row incs 4 sts - just inside the edge sts at the beg and end and one on either side of the center stitch. The cast on and sides of the row form the top edge, the sts on the needle will be the bottom edge where you sometimes knit a border pattern.
This article and free pattern
explains it a little better. And you do follow a chart from R to L on the RS rows and usually it's plain purl or knit on the WS which might not be charted. Some charts only show half from the edge to the center st, then you either repeat the row again or reverse it, reading from L to R, but it should say what to do in the text pattern.