Hello and welcome to the forum! Let me explain this.
The category that you are talking about is called pixel art. Other “categories” are Trail Art, music and so on.
To make these artworks, you need to use trails or clones. Every clone or dot represents a pixel. Pixel arts are based on often thousands of pixels to make it realistic - but you can start small as well and make something simple. There are pixel arts with just about 20 pixels and even less that can look amazing!
Pixel arts can be done in more different ways that just “trails” and clones. There are different types of pixel arts like smooth pixel art, dot pixel art and more. There are really good tutorials on the forum about this. Here are some good tutorials that you can read or watch: