略知皮毛[ lüè zhī pí máo ]

⒈ 比喻稍有一些表面、肤浅的认识。例何况我们不过略知皮毛，岂敢乱谈，贻笑大方！——清·李汝珍《镜花缘》英smattering; have only a superficial knowledge of a subject;