LWJGL is a lightweight game development library that does not contain a built in physics library. In order to get jumping and gravity to work only using JOML and LWJGL, you will need to create your own collision detection and physics integration code which is too complicated to be explained here. If you want to do that, there are plenty of books on the subject. However, if you are new to programing or do not have much interest in physics programing, I recommend finding an additional physics package or using a full game engine which includes physics code.