不但(不仅）……而且 表示递进，这是固定搭配，just like "not only…… but also" But it emphasize the latter, EG:不但要爱护工具，而且要节省材料，In this sentence, it means taking care of the tools and saving the materia are both important, but the saving is more. Sometimes 不仅、不光、不只、不单，mean "more than" for example,这不仅是我个人的主张。That means there are someome else who agree with me. It's what I think,maybe there are some mistakes~