Meditation seems simple, and for some it is.
Most meditation practices involve sitting, closing your eyes, and being aware of your breath, body, and thoughts ... without judging them.
Meditation is different than just sitting around, because there is an intention of being still, mindful, aware, and nonjudgmental. It's different than yoga, which is a movement practice typically centered on awareness of the body, and less so thoughts. Prayer is tied to the idea of a higher power, whereas meditation typically is not.