Move the object with the lower vertex at Z = 0 - Modeling - Blender Artists Community
How to move the origin of an object in Blender - YouTube
10 Essential Tips: Optimizing Your Blender Workflow Using the 3D Cursor - CG Cookie
So, I cannot move objects anymore, when I select anyone, these 3 axis arrows appear, and if I press G, those arrows will move, but not the object itself. I've been using
Blender tutorial: selecting and transforming objects