Knitting in the round isn't as scary as you might think. In fact, I actually prefer it to working flat most of the time. Because (a) there's less seaming, (b) there's less purling and (c) ... there's less seaming. (I don't like seaming. Maybe you guessed.)
In its heart and soul, circular knitting isn't so very different from the flat variety. Stitches are still made the same way you're used to, though the way you combine them may change. For instance the way you make garter stitch and stockinette is exactly backwards from the way you'd do it when working flat. In other words, stockinette in the round is knit every stitch, while garter stitch requires you to purl alternate rounds. That's confusing at first, until you get your head around the concept that you're only actually making one "row" -- it's just one that spirals from one end to the other continuously, like a Slinky.
Patterns are usually intended to be worked either flat or in the round (some may include instructions for both, but I haven't encountered any like that), so the pattern will tell you what you need to know in the way of how many stitches to cast on. You'd only run into a bump in the road if you were making up your own pattern or converting one that was written for a flat piece to one worked in the round. But since you're not doing either of those things yet, it's probably best to defer learning that until you need it.
But patterns written for circular knitting (usually) will tell you to "join in round". I'm not fluent enough in patternese to know if that means anything more than "Start knitting at the beginning of the CO round (rather than the end of it after turning the work over)", and there may be something fancy-schmancy that people do here, but I never have. (Exception: Magic Loop, but you won't have to do that with a cowl -- unless the cowl is for an ostrich or something.) There's a "step" (or "jog") that's created where the first CO loop meets the last stitch of the first round, but that's easily fixed with a crochet hook and the CO tail. (Same is true at the BO end.)
Just keep calm and carry yarn.