You can also see that the pad moves relative to it's 'center' position, so if we place the pad at 0 x 0, it would actually extend 0.3mm out in every direction.
This is very important to understand when placing pads. A 0.6x0.6mm pad placed at 0 x 0 would actually start at X -0.3mm and Y -0.3mm and end at X 0.3mm and Y 0.3mm!
Generally the easiest way to start placing your pads, it to place a single pad at the 0 x 0 position, which we'll refer to as the 'home' or 'zero' position.
Place a 0.6 x 0.6 mm pad at the home position by selecting the Smd tool, setting the size, and then simply clicking the mouse at 0 x 0, which is indicated by a small white '+' on your grid:
We can see in the image below that we are on a 0.1 (mm) grid, and the mouse is currently at -0.4 x 0.0: