I'm extremely new to 3D modeling, just started today actually. But there have been some problems with the boolean modifier that I just cannot google my way out of. First, when I'm trying to carve out a chunk instead of making a hole right through an object, the two meshes just combine instead of subtracting. The second is when I finally get it to work it leaves my object a hollowed mess. In the screenshots, you can see the left object is the one I want to keep, and the right one is what I want to subtract from the left one. If I select Difference the objects just combine, but if I select Union I get what I actually want but the resulting object is hollow and with some weird planes all over the inside. How can I fix these problems?
You have the right operation i.e Difference, and it is working too, the problem with it is John Cena(you can't see it). Jokes aside!
You only can't see the changes because the object is lying on it. If you want to see the changes before applying the modifier, select the object which you are using for hollowing and go to Object Tab. Under View Port Display Select Display as Wire! Now you can see the hollow.
And also after applying the modifier you can delete that hollow helping object to see the hollow. But its risky, arrange it first with the above method and then you are ready to apply and delete.