
I wish that picture had jumped up on the internet when I replied earlier; I'd have posted it then. It even has the right hammer. The "hammer" is the unlabeled part between the "Rear Notch Sight" and "Manual Safety" in the picture. I'll keep it simple because there're so many other people who know it better, and much better info out there.
The grip safety does what it says in the name: if you haven't compressed the grip safety, which can be accomplished by gripping the thing exactly like it looks like it's designed to be, then the trigger won't release the hammer and the firearm won't fire. It's wordier to explain than it is to show. To use a 1911, put ammo in the magazine, insert the magazine into the pistol, charge the weapon by pulling the slide back and releasing it. Pulling the slide back will cock the hammer. If you don't intend to fire it immediately then flip the manual safety up. Now's it's "cocked and locked" and can be safely holstered and carried. To fire from that position the grip safety has to be squeezed, the manual safety has to be moved down (like in the picture), and the trigger pulled. It sounds like a lot, but all the switches are right where your hands/fingers go if you happen to be John Moses Browning. I've read one internet anecdote of someone involved in an altercation and had the misfortune to get shot in the hand and couldn't return fire due to not being able to engage the grip safety. Take that for what it's worth. To anyone interested in buying their first firearm to use, I do not recommend a 1911 because there's a step in the manipulation where the safety has to be off with a cartridge chambered to load it.