If the ball has ever hit you on the legs when fielding you'll know exactly why you wear pads when batting.
Their job is protection. Make sure they fit comfortably and properly as you need to move quickly when nabbing those quick singles.
The horizontal panels on the front of the pad should be at knee height, with the top of the pad covering up the lower thigh.
Most pads have three velcro straps to fasten them to your leg, making them easy to adjust.
Modern pads are incredibly light - but are still able to provide plenty of protection.