The threads are smooth and strong and come in various colors. Another good option is Gutermann; they’re a bit more premium but worth it if you want something that’ll hold up well over time. You can check out their website for more details: manufacturer's website. You might also want to grab a few spools from both to see which feels right. Once you get a feel for it, you’ll find what works best for your projects!
This post has been up for a while, but it's still worth bringing up As a beginner, starting with a reliable brand is best but not too expensive. I like using Coats & Clark threads—they’ve been around for ages and are pretty easy to work with.