One of the most important part of every camera is its lens. The main difference between them is focal length and aperture. The focal length essentially determines how zooned in your photos are and the aperture determines how much light will go through your lens to the sensor.
Like I already said, focal length determines how zoomed in your photos will be. The smaller the focal length is, the wider the photo will be. They say that the standard focal length, that shows the same angle as we see it with our eyes is 50mm on full frame sensor or around 32mm on cropped sensor. Everything that is below that could be called wide angle and everything above that zoom.
We can say that on full frame cameras focal length under 24mm means ultra-wide lens, 24-35mm wide lens, then between 35mm and 75mm standard lens, 75-150mm zoom lens and anything above 150mm telephoto lens.
A lens’s aperture determines how much light it lets through. More often than not, a wider aperture (lower f-number) is preferable, as it will allow you to take photos in situations with little or no natural light. A wide aperture also allows you to use a faster shutter speed, which is important when photographing fast-moving subjects or when hand-holding the camera.
Most camera’s lenses nowadays have a built-in autofocus mechanism which takes care of getting sharp photos. Some lenses employ more advanced focusing systems that can be needed in particular situations, like silent autofocus where the lens sound can alert the subject and potentially ruin your shot or internal focusing where the outside of the lens stays perfectly still, which can be beneficial in macro photography where any movement could scare your subject away.
Camera movement can cause blurring in your photo at slow shutter speeds. Image stabilization (IS, OS…) is designed to reduce this, making your shots sharper and allowing you to shoot at slower speeds without using a tripod.