The above photo is of a pistol made by a VERY well-know gun manufacturer. When people think semiautomatic pistols, this comes to mind. All pistols will not be the same, but this will represent a good majority of polymer frame, striker fired pistols. Now let's get into the working parts that you need to become familiar with.
There are two main components to a handgun.
Frame: This is the part of the handgun that you hold when firing. Usually it is made of polymer or steel. It is composed of the grip, magazine well (where the magazine is inserted), trigger guard, which surrounds the trigger, and sometimes a rail, which is where accessories can be mounted. Also, the back of the grip is called the backstrap. On some handguns, it can be changed to give the shooter a better feel of the handgun. The takedown lever and slide lock (not pictured) are also located on the slide. They are used to disassemble the handgun and keep the slide locked in the rear position, respectively.
Slide: This is the part of the handgun that moves back and forth on the slide when fired. The force of the slide is what causes the felt recoil or "kick back" when shooting. It is where the front and rear sights are located. Also, the slide is where the extractor pulls out spent (fired) shell casings. The casings exit the firearm through the ejection port. Notice in the photo there are grooves cut into the rear of the slide. These are called serrations. They are intentionally cut into the slide to allow the user to get a better purchase (grip) on the slide when chambering a round. Finally, the barrel of the handgun is located in the slide. The end of the barrel, where the fired projectile exits the handgun, is called the muzzle.
Side Note: "striker fired" is a term used for the way the primer of a bullet is engaged in order to ignite the gun powder and fire the projectile. This is oppose to say, a hammer fired weapon. Don't worry, all this will be explained at a later time. Stay tuned.