So let's explore some easy projects for a first time circular knitter.
You've already got a lot of options ahead of you because when you knit circularly you don't have to seam anything, you don't have any wrong sides to worry about, so it's actually easier to start circular knitting than it is to start by using straight needles.
The first project I would recommend is a headband.
This is a super easy project that's available on my website. And it's easy because you cast on, you knit straight, and then you cast off. There's no shaping involved at all. If you wanted to even omit the color work part, you could.
This is great because there's no shaping. The number that you cast on is the same number of stitches you have when you cast off. You're just using a circular needle to not have to sew anything up and to never have to knit the wrong side.
So that's a great first time project.
Then you might be ready to move on to something that's knit exactly the same way but in a larger diameter like an infinity scarf.
This kind of scarf you can wrap around your neck several times. And it's easy.
Here's another circular scarf. It's easy because the number of stitches that you start with at your cast on edge are the same number of stitches that you'll bind off at the end. No shaping involved at all.
The next project you could do is something that does require a little bit of shaping.
You could do a hat, which starts straight and then starts decreasing. You can't do on a 16 inch circular but you can do on double points or on two circular needles or on the magic loop method. So this is for when you're ready to branch into some shaping.
And then finally you can move on to a hat that has a special stitch pattern or some kind of design in it where you would start casting on a number and then you would do some shaping in the stitch pattern as you go.
So those are some ideas for first time circular knitting. Some easy projects for you to get your feet wet with.