When you get started with Java or Android, you quickly learn that (0,0) is in the top-left corner. In LibGDX, however, (0,0) is by default in the bottom left corner.
Using an Orthographic camera, you can get (0, 0) to be in the top-left corner. Though by default, (0, 0) is in the bottom-left corner. This is something that is important to know, as it also changes which corner of the textures have the X and Y coordinates.