Many folks see the Cavarly on TV or the movies, You've all seen the soldiers that ride horses, but Cavarly is a mission, or more particularly a set of missions that defines a particular job on the battlefield. Basically, the role of Cavalry is simple: to protect the main force, provide screening, reconnaissance, raids, deception and defense. The Cavalry can be used in the attack, but that's not their main role.
You can click over to the Cavalry School and read all about the missions, The great Cavarly commander simply considered the horse a mode of transportation. Cavarly is mobility, and once you get off the horse, you become infantry. Nowadays the Cavalry rides armored vehicles, or helicopters, but the mission remains the same.
Two great clips from YouTube. The first, LTC Hal Moore introduces his officers to the helicopter.
LTG Moore died recently, but as far as I know, while he served in the Cavalry, he indentified more as an Infantry officer. He knew the role of the Cavalry, and fought one of the more famous Cavalry battles of the modern era.
One of the great Cavalry officers of the Civil War was John Buford. General Buford, probably more than any other man in that conflict, understood the role of Cavalry. Buford is credited with providing a screen for the main force, providing reconnaisance, and denying Harry Heth the high ground in the opening engagements of the battle at Gettysburg. The clip below best explains the role of Cavalry during an opening engagement.
UPDATE** I originally embedded the wrong video. Here's the one I intended to embed. After editing, I realize that in both of these clips, Sam Elliot plays leading roles in both these movies. Still, the clip below is longer and gives a better indication of the role Cavalry plays in the lead-up to battle. John Buford is credited as sying that the horse is only a mans to move to battle. Once you get off your fine, fat horse, you're infantry.
I never get tired of watching it.