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Semi-automatic, caliber, magazine capacity; terms you've heard repeatedly in the last couple of days as we've reported on the shooting spree in Virginia. But, what does it all mean?

For those of you who know little about guns, below is a breakdown (or a 101 lesson) on the guns used.

But first, here's an overview: Virginia Tech shooter Cho Seung-Hui used two guns to kill 33 people, including himself, at Virginia Tech on Monday. CBS News Chief Investigative Correspondent Armen Keteyian was the first to identify and report the Roanoke gun store where Cho bought one of the weapons.

Today, a law enforcement source confirmed to the CBS News investigative unit that Cho purchased the second gun online and then picked it up at store in Blacksburg.

1. Walther P22

Interestingly, both the guns used in the deadliest school shooting in US history were made in Europe. Walther P22 is a handgun manufactured in Germany and distributed in the US by a company called Smith & Wesson based in Springfield, Massachusetts.

Sold at most gun stores, it costs about $300 to $400 and its magazine capacity (in other words, how many rounds or bullets it can hold at one time) is 10. In addition to the 10 rounds in the magazine, it can hold one more bullet in its chamber for a total of 11 before needing to be reloaded.

It is a semi-automatic, which (if you don't know) means it can fire one shot each time the trigger is pulled, and is a .22 caliber firearm. Caliber refers to the diameter inside a barrel which is expressed in millimeters or inches (depending on the type of gun.) The bigger the caliber, the bigger the bullet.

But, get this: the Walther P22 is typically used for recreational shooting and is thought of in the gun industry as more of a target practice pistol. Experts say one reason is that the ammo is cheap. You can get 500 rounds for about $14. Furthermore, the caliber is not as high as guns normally used for self-defense. Many police officers, for instance, carry .45 caliber firearms. Philip Van Cleave, president of the Virginia Citizens Defense League, says "it can kill, but you'd have to hit someone in a vital spot with an exact shot."

2. Glock 19

Like the Walther P22, the Glock 19 is a semi-automatic pistol sold just about anywhere you can get a gun.

Glock is an Austrian manufacture with its North American base located in Smyrna, Georgia. Company spokesperson Carlos Guevara, told me the model 19 pistol is the company's third biggest seller priced at about $500 to $600.

Unlike the .22, this firearm is typically used for self-defense and can easily be concealed. It can hold 16 bullets total at one time with its designated magazine of 15 rounds, plus 1 chamber bullet. But, magazines with more ammo can be inserted into the Glock 19 like the magazine used by the military which can hold 32 rounds.

It's unclear what kind of magazine Cho had. But, we do know he purchased 1 box with 50 rounds of ammo for $10 along with his Glock. If he used the designated magazine and fired all 50 rounds, he would have had to reload at least 3 or 4 times.

The Glock 19 is a 9 mm (millimeter) weapon which compares in caliber to a .38 pistol. The company website labels it an "all-round talent" used by "elite pilots…for their efficient defense in emergency situations." It is supposedly a popular, reliable, quality gun that, of course, can be deadly.

But no matter the type of firearm, I've been told repeatedly by gun experts that the precision and speed in which a shooter can reload and fire a gun plays a huge part in how deadly a shooting rampage can be. Now, with more information coming to light about Cho's disturbing mental state and watching the video he sent to a news outlet, it seems he was determined not to fail, powerful gun or not.