The main apparatuses to choose between as a beginner are: aerial hammock (slings), hoop (also called lyra), static trapeze and silks. If you’re strong and confident, you could immediately consider straps, rope (also sometimes called corde lisse) or flying/dynamic trapeze, but otherwise I’d advise against it.
In all cases, make sure that the studio and class you’re taking accept beginners of your level. That should be clear from the class description, but you can also call the studio to check. When you get there, let the instructor know it’s your first class, so they can teach you appropriately.
In general, it’s a good idea to try several apparatuses, as that’s the only way to really see which ones you enjoy. Some studios even offer taster (or sometimes conditioning) classes where you can try a bit of each. Most of the time the way the class is taught is much more important than the apparatus itself. A well-taught beginners class of any apparatus should build up your strength while having fun. Sometimes you might not vibe well with the teacher; it’s worth trying the same apparatus with a different instructor if you have the option to.
Perhaps the easiest introduction to the world would be aerial yoga, which is performed on an aerial hammock. That is less about tricks. There’s little climbing and basic inversions are much easier (if you’ve never inverted before, this can be a good place to try for the first time. It’s more about leaning back and overcoming fear than pure strength). It will still build your strength and flexibility, but not quite in the same way as other disciplines.
Aerial slings can be similar to yoga, but also a step closer to silks. It also uses the aerial hammock, but the base might be higher up than for yoga. It’s often considered a more entry-level class, but in my experience that depends on how it is taught. In general I’d still recommend it as a starting point.
Aerial hoop can be a very good place to start. There are a number of ways to get up on the hoop, so even if you can’t manage a pike from the start, you can learn to progress towards it, for example either by using your feet, or coming up on the hoop from the side. Once you’re in the hoop, there’s quite a few beginner-level moves you can practice while you build up strength towards more advanced ones. One drawback to hoop is that it is particularly rough on your hands, and can hurt in other places too.
When starting out, static trapeze can be similar to hoop. The bar is narrower, which limits certain moves. You’ll have to get used to ropes, but that can be beneficial if you want to move towards that next.
Not everyone would count this under aerials, but there are lots of similarities, so it’s worth mentioning pole dance. Pole is more widely spread than aerials, so it can be easier to find a studio and beginners classes. Because it has a bigger community, classes can also be structured better and progression more defined. Skills like climbing the pole and inverting translate well to other apparatuses after you get used to a different texture. If the circus courses in your area are too intimidating, pole can be a great place to build up strength.
I hope that was helpful. As a summary, my top pick for a first circus class would be hoop or slings. If you consider a more wide range of activities, I’d start with aerial yoga or pole. But do try them all out to see what you like best!