You should make sure that you can see the Edit Panel. The Edit Panel is a box information running along the left side of the screen. If you do not see the Edit Panel, select View Toolbars Edit Panel. Now that the panel is visible select the Add Pin tool. Look to the top section of the Edit Panel you should now see pin properties. For a non-plated hole select the non plated box then select a Hole Size from the drop down menu. Now you can place a non-plated drilled hole on your layout.
If you want a plated mounting hole, uncheck the Non-Plated box. You can now select the Holes size from the drop down menu. You also now have options to change the pad geometry to either a round, square, or oval pad. Once the pad geometry is selected you can then fill in the Pad Width and Height. If a round pad geometry is selected you will only need to fill in the Pad Width field.