1) There is no such thing as a stupid question.
2) Simply put, your throttle more or less controls the fuel flow being sent to the engine. You can see it like a gas pedal in a car. Throttling up or down will have an effect on your engine RPM and, more importantly, your manifold pressure (also called Boost Pressure, MP or ATA). This manifold pressure is expressed in units of pressure (US aircraft: inches of Mercury (Hg), British aircraft: Psi or "pounds of boost", German Aircraft: Atmosphere, Russian aircraft: mm of Mercury (Hg)).
In general, applying more throttle = getting more power.
3) The RPM Control Lever (also called Propeller Pitch Control) controls the propeller pitch. A good analogy is switching gears on a bike or a manual car. The history of these "RPM controllers" is long and fastidious. At first, pilots realized that they could tweak manually the pitch of their propeller, and that their aircraft performance would be better at certain RPM. A "fine" pitch would allow the engine to develop a higher RPM, which allowed the aircraft to climb much more easily. However, a fine pitch and high RPM has the side-effect of consuming a lot of fuel and wearing down the engine at a quicker rate. Oil temperature and coolant/glycol temperature can easily go beyond recommended limits if you stay at max RPM for too long, which can have dire consequences (radiator perforation or even worse: complete engine seizure). A "coarse" propeller pitch and low RPM, on the other hand, is much more useful if you are going straight and want to gain speed. It will also help you save on fuel. A coarser pitch can be useful in a dive to prevent engine overspeed, but it is not recommended in a climb. So, as you can see, the pilot would change his propeller pitch based on 1) his engine RPM 2) his oil/coolant temperature 3) what he wants to do with his aircraft (climb, cruise or descend) 4) surrounding air density, which varies with altitude (the higher you go, the less air you will find) and has a direct incidence on the thrust generated by the propeller and the engine.
In most flight manuals, you will find many different power ratings (MIL power, TOGA (Takeoff-Go-Around), FULL power, 5 MINUTE power, 1 MINUTE EMERGENCY power, WAR EMERGENCY POWER (WEP), etc.). Most of the time, these are power settings that you can only maintain for a certain amount of time before either your engine blows up in your face. In most aircraft guides, I always recommend certain power settings (basically set your throttle and RPM controller in order to reach certain RPM and Manifold Pressure values and you'll be fine) based on certain situations. In certain aircraft, you can also use MW50 (50-50 mix of Methanol-Water) which can be injected into the engine to improve performance.
Take note that eventually, engineers found a way to create a "constant-speed propeller" system that allowed that pilot to set the pilot to set his engine to a desired RPM, and the aircraft will vary the propeller pitch automatically to try to maintain this desired RPM. This is what most Russian aircraft in BoS and BoM have at the moment, with some exceptions. The Germans, on the other side, found a way to create a propeller governor that will automatize even further the engine. For instance, in the FW190, with a single throttle you can control your manifold pressure and the RPM will automatically set itself to the optimal value. This reduces the pilot's workload. This governor is also installed on the Bf.109, but you can also set the propeller pitch to a "manual" mode if you want in the 109 only.
Today, most modern aircraft have a similar governor. Engineers eventually found even more efficient ways to control the engine with a FADEC (Full Authority Digital Engine Controller), which is basically the "brain" of the engine that controls most engine parameters automatically by controlling fuel/air valves within the engine system... so you only have to deal with a simple throttle.
So, overall, you can control your engine RPM with both your throttle and the RPM control lever. I typically set my manifold pressure first, and then I fine-tune the RPM with the RPM control lever to reach the desired RPM and MP setting. You will also have to keep an eye on your oil and coolant temperature: you can control these temperatures using your coolant and oil radiator or cowling flap open/close controls. Your airspeed and airflow going through the engine will also have a direct influence on your engine temperatures (the faster you go, the more airflow goes through the engine to cool it down).