Assuming you're asking about American football shoulder pads, the answer is relatively simple. Most of the time, you can just remove the pads from your jersey and wash them in a sink with some soap and water. You can also put them in a mesh laundry bag and wash them in your washing machine on a delicate cycle.
If your shoulder pads are particularly dirty or smelly, you may want to soak them in a tub of warm water with some vinegar or baking soda before washing them. You can also spot clean them with a damp cloth and some mild soap or detergent if they're not too dirty.
Once your shoulder pads are clean, be sure to air dry them completely before putting them back on your jersey. You don't want to risk ruining your jersey by putting wet shoulder pads on it!