Most SLR cameras come with what is known as "kit lenses". Usually they include a short lens (18-55mm) and a telephoto lens (100-300mm). Since baseball infields are fairly large (90' bases) it is recommended to use the telephoto lense to reach everything around the entire infield.
These lenses are variable aperture lenses, meaning the more you zomm the smaller the aperture becomes. This will not affect your photos much until it becomes darker. With entry to mid-level cameras, when the lights come on you are not able to get any good quality images so get your shots early in the daylight.
Softball, even though the infield is smaller, still requires the long (100-300mm) to cover all the action.
Entry level cameras have pre-sets so you can select the settings for what you are photographing. The "SPORTS" setting is designated by a little running man figure. This tells the camera to select the fastest possible shutter speed and the widest aperture available to "stop the action" so the picture is not blured by the motion.
With more advanced cameras or manual settings the general rule is never shoot a shutter speed slower than the maxamum focal length of the lense. e.g. 300mm = 1/300 of a second. For action sports the shutter speed should never be lower than 1/1000 of a second.
Advanced full frame cameras are capeable of shutter speeds as fast as 1/8000, although that is a bit excessive. My personal target is between 1/1000 and 1/3000 of a second.
The sample images you will see in these mini-lessons will include the camera information to give you an idea what is required for top quality images.
The Running Man icon will look something like this