Just turn it on and glide it through the area you want to trim!
You can use it with the guide comb or directly on the skin for a closer trim. Always ensure you angle the shaver so that the trimmer head and blade are parallel to the skin. It will then glide smoothly avoiding nicks and tugs. Please do not hold it directly perpendicular to the skin (i.e. stabbing position).
You can find a step-by-step detailed guide here, and a quick demo here.