They're knife pleats, which are probably the easiest but have the disadvantage of asymmetry, if that's important to you.
For my next pleated skirt, I will advance a level and try out box pleats. Maybe on a larger doll though, so I don't have to make teeny-tiny folds everywhere. American Girl-scale wouldn't be too hard.
Worst part of making this : I pleated, and then hemmed. Why? I don't know. I guess I got so into the idea of "hey, let's do pleats!" that I forgot skirts needed hems too... This made sewing the hem quite painful. I need to remember to HEM FIRST.
Not a good look, so I generally leave the skirt a bit higher, as in the first picture.
For the next skirt, a waist-sized waistband would be best.
You can see more clearly here that I didn't use the right thread color. (It's visible on the hem in the above pictures as well.) I need to pay more attention to things like that.
Poor Eun-Jae still doesn't have a proper shirt!