Raycasting with camera for collisions


I’m trying to create a first-person demo with collision detection in all axes so the player collides with boxes and can jump on them. I’ve spent the day researching this and all the methodsv(e.g. Lee Stemkoski’s) seem extremely long and complicated (at least to a three.js beginner). However, in this official example the player is able to jump on the boxes, and the code for it is so short. So I thought that the rest of the collisions should be just as easy and/or short to do. Can you please give me guidelines for what to do? I don’t understand any of the code, so it is hard for me to do, despite having read the raycaster docs.
Any help is appreciated.