So this will probably be a multiple part post because there is just so much to cover, however I will be posting the first part covering the basics before making the "Building An Arsenal on the Cheap" post.
Double Action/Single Action: This is one of the more common types of handgun trigger types, the first trigger pull is rather heavy with the following trigger pulls being very light. E.g. 8 pounds for the first pull, 4 pounds for the remaining pulls until the firearm is empty. Many guns utilize this type of action to get around the need for a manual safety. The operator can just draw the firearm and squeeze the trigger.
Grain: You'll often see ammunition for sale labeled as "9mm 124 grain". The grain (like I thought for a long time) does not mean grains of gun powder but rather grain as in the weight of the projectile.
Polymer: You'll see the word polymer used when discussing many modern handguns. Polymer came into handgun use with the HK VP70 and is still common today. Polymer is a very strong and light material that is perfectly suitable for a firearm.
Picatinny Rail: This is a rail on the front of the pistols frame that allows you to attach accessories such as lights, lasers, and even pistol bayonets.
That about covers it today. I kept it short so I could move on to the next post.