SlideMagic picks a suitable font size when you start typing text in an empty object. With the "+" and "-" buttons in the object menu bar you can adjust the object's font size. The smallest font size in SlideMagic is 8, the largest is 96. For good readability of your slides, a font size of 18 or higher is recommended.
When the size of an object changes (via the EDIT OBJECT SHAPE, or GRID modifications) the font size is adjusted automatically by the application. Larger objects get bigger fonts and vice versa. You can correct the decision of the application afterwards manually.
Text in an object can be aligned left, right, or centred, and aligned top, middle, or bottom. Just press the corresponding buttons in the object menu bar.