You can magnify images by clicking on the magnify tool from the toolbar (it will say 'Zoom Tool' if you hover over it). You can also magnify images by keeping your finger down on the CTRL key whilst pressing either the '+' key or the '-' key. This is useful so that you don't have to deselect your current tool. For example, if you were already on the brush tool and you wished to magnify an image, then you can use the keys to magnify the image rather than having to switch to the magnify tool.
If you are using an eMac and you wish to magnify an image in PhotoShop, then you can use the apple button. This is the button on your keyboard which has a picture of an apple on it.
If you are using an eMac and you wish to magnify an image in PhotoShop, then you can use the apple button. This is the button on your keyboard which has a picture of an apple on it.