Summarize:

Remove the old lens from your camera, either by pressing a lens release button or twisting the lens off. On 1 end of the 50 mm lens, you should see 2 marks. Align these with the corresponding marks on the camera and press the lens down. Turn the lens clockwise until you hear a click. Lenses may vary based on the manufacturer. For more instructions on how to attach a lens to your specific camera, read the manual that came with your camera. In most cameras, you will do this by turning the dial to “M” or by pressing the “Mode” button. Manual mode allows you to choose your own shutter and aperture settings. Once you are in manual mode, the screen of your camera should allow you to select both shutter and aperture settings. Refer to your camera's manual for more instructions. Shutter speed is the length of time that the shutter is open. It is measured in fractions of seconds. The general rule for shutter speed is to divide 1 by the focal length of the lens. This is the slowest shutter speed you should use.  Use a faster shutter speed, such as 1/125 or 1/250, to catch fast moving objects like cars or birds. If you want more blurred movement in your photograph, choose a slower speed, like 1/60. If you're in a dark or low-light area, choose a shutter speed of 1/250 or faster. Aperture affects the exposure (or brightness) and the focus of your photograph. A larger aperture will have more background blur and a brighter exposure. A smaller aperture will have less blur and a darker exposure.  Apertures are measured as "f stops." The smaller the number, the larger the aperture is. For objects that are far away in normal light conditions (such as landscapes, architectural photos, or group pictures), select an aperture of f4 or f5.6. If you’re working in low-light conditions or close up (such as portraits or still life), use a f1.4, f1.8, or f2.8 setting.
Attach the lens to the camera. Turn your camera to manual mode. Change the shutter speed to 1/50 or faster. Adjust your aperture settings.