A helicopter is a "rotary winged" aircraft. Instead of a fixed wing (the "plane" bit of the word aeroplane) on each side of the aircraft, a helicoptor has 2, 3 or 4 "wings" which are constructed like a very large propellor and mounted on the top of the aircraft. These "wings" rotating like a propellor create the lift and thrust required to make the aircraft fly. This gives it an ability, not only to fly forwards, but also backwards and sideways, and also to fly vertically up and down. It is the last of these which is perhaps the main reason for their invention and development. They do not need a runway in order to fly. Helicopters also have a small propellor at the tail - the "tail rotor".
For a start of course, you need a computer with keyboard and screen, flight simulator software, and - a lot of patience. For hardware, forget trying to fly with just the keyboard, or even a yoke - you will find flying rotary winged aircraft next to impossible. As a minimum you will need a 4 axis joystick - often called a "twist grip" joystick, in which the rudder of fixed wing aircraft is controlled by twisting the joystick handle. With just a joystick of this type, short flights can be made before the pressure of the inbuilt springs becomes uncomfortable. This is because flying helicopters requires constant forward pressure to hold the nose down, twist pressure to keep straight and sideways pressure to prevent the aircraft tilting to one side as it flies. If you get airborne, and let go of the joystick - i.e. all controls neutral - it was crash very quickly.
The flight controls of a helicopter are almost totally different to those of a fixed winged aircraft. "Almost" because a helicopter still has foot pedals. The other two controls are the "Collective" and the "Cyclic". They both control what the "main rotor" (the big propellor on top of the aircraft) does. The main rotor speed of rotation is controlled by a governor and only changes by a small amount in flight. It is what the blades are doing which predominantly controls the behaviour of the aircraft.
The paragraph above is the theory - now for the practical. With a gaming joystick, the handle is the Cyclic and the pedals. Axis 1 (forward and back) controls pitch, Axis 2 (side to side) controls roll. These two axes act as the Cyclic. The twist action, Axis 3, controls yaw and simulates pedals. Axis 4, the throttle lever, is the Collective. The joystick handle is spring-loaded, and this creates a problem, because when flying a helicopter, to go anywhere you have to push the stick forward and hold it there to move forwards and twist it a little to maintain direction. After a while this becomes too tiring and control becomes erratic. For FSX pilots, a utility called Helitrim can be downloaded from Avsim.com which allows the pilot to fly with a joystick in a neutral position - no strain on the wrist - whilst being able to "trim" the pitch, yaw and roll controls so that the aircraft flies in a stable manner. Helitrim does not work in X-Plane.
The next step in realism is to add pedals. By using pedals, the "twist" action (axis 3) is no longer needed, so some of the pressure on your wrist is relieved. The pièce de resistance though, is a separate throttle control to replace axis 4. This separate throttle control can be either a commercially available unit (which comes with mixture and propellor levers too for fixed wing aircraft flying), or you can plug in a second joystick and use just the throttle from that one. Now you can replicate the full helicopter controls, and comfortably fly for longer periods, although you still may need to hold the joystick handle forward when flying forward, unless the helicopter you are flying has sufficient pitch trim range to eliminate any necessary forward pressure. It is even better if the helicopter has an autopilot for the long hauls.
For Flightsim software, in the Microsoft heritage group you currently have the choice of FSX, its cousin the Steam Edition version FSX-SE, and Prepare3D, although the latter is not licenced for "gaming". Then there is X-Plane. X-Plane is in constant development for the life of the version, unlike the others, plus it has more realistic flight dynamics, and payware quality freeware helicopters.
There are several well written tutorials out on the web.
I myself have been doing it exclusively for about 18 months, finding the right helicopter for me and honing my skills. It is not just a matter of taking off, and flying from A to B. Normal flight rules are obeyed, both on the ground and in the air in addition to controlling the machine. I find it far more satisfying than sitting in a cockpit at 35,000 feet watching the clouds roll by beneath me. The fun is in tucking that ship into tight spaces in the middle of nowhere. And of course, you are not restricted to SIDs and Stars either. You can fly Search and Rescue missions, or land on oil rigs out in the ocean, deliver supplies to lighthouses (in some cases landing on top of them!), even service Navy frigates and aircraft carriers. I have done them all, but it does take time and a lot of practice to master those skills. So give it a try, but do not give up too soon. Get the right Helicopter and hardware setup, and the world is yours. No need to land at airports if you don't want to, of course. If you have any queries, you always catch me, Frank Fisher, on the CIX forum or via a forum Private Message. HAPPY FLYING.