A revolver, sometimes called a wheel gun, has a cylinder which holds multiple cartridges and rotates each cartridge into firing position as the action is worked.
In a single action revolver the action is worked with the hammer. The trigger serves only to fire the gun.
The classic single action revolver is a six shooter. This is due to its historical roots not to any technical considerations. Double action revolvers chambered for .22 rimfire often have eight shot cylinders and compact revolvers often have only five.
Most revolvers do not have an external safety, but I have seen some that do. Read the manual.
A single action revolver has a loading gate to the right of the hammer. The hammer has three positions: down (uncocked), half cock, and full cock (cocked). Half cock is the first position you reach as you pull the hammer back. In this position the cylinder will rotate freely to allow loading and unloading. To check if a single action revolver is loaded:
Once the hammer of a single action revolver is cocked, or half cocked, it can not be lowered without releasing it with the trigger.
Obviously if the hammer drops on a live round the gun will fire. The hammer must be lowered in a controlled manner while pulling the trigger.
From the half cock position it will be necessary to pull the hammer back slightly to disengage it from the trigger.
Put a thumb or finger of one hand under the hammer, while pulling the trigger and controlling the hammer with the other hand. Ease your finger out and let the hammer down gently.
Keep the gun pointed in a safe direction at all times!
The cylinder rotates around a pin. To remove the cylinder, the pin must be removed. The Ruger Single Six has a button on the left side just forward of the cylinder which releases the pin. Some Colt models have a button, other models have a screw. Your revolver might be different. Read the manual.
Early revolvers had the firing pin on the hammer. Some still do. The difference is whether or not the firing pin sits on the primer when the hammer is down. If it does, the revolver may fire if dropped or if the hammer is jarred. Revolvers of this type should be carried with the hammer down on an empty chamber.
Many newer revolvers have some kind of mechanism to prevent the firing pin from striking the primer if the trigger is not pulled. While this is a nice feature, remember, mechanisms can fail. They are not a substitute for vigilance.