How the train driver turn train on curves?

That's it!! very observant, most locomotives nowadays have power steering, you can imagine how difficult it would be otherwise.

The wheel is not for steering, it is the handbrake. The train is not steered. It follows the curves. Most train carriages nowadays have bogies (aka trucks) at either end which pivot as the train negotiates the curve. These give a smoother ride than a rigid wheelbase vehicle and also allow the superstructure of the carriage to be longer. The treads of the wheels are tapered to allow for the difference in speed of the inner and outer wheels when riding on the curve, the inner wheel presents a smaller circumference to the rail than the outer wheel and this helps to reduce wear and tear on both wheel and rail. The wheel stays on the track because of the flange - the rim on the inner surface of the wheel which is of a larger diameter than the tread.

fitted to the loco's driving wheels of the loco,are what's known as 'tyres',they locate to the inside of the rail,keeping them on the rails. http://en.wikipedia.org/wiki/History_of_rail_transport

Trains are on rails...they dont use steering wheels...that was probably a valve or a brake....and seriously? this shouldnt even be a question

In real terms, this can be a brake. If the emergency brake AND the air brakes fail, this is a last resort. In german trains, this is the throttle

Depending, that small wheel near the engineer's (train driver's) seat is a rheostat used to control the flow of electricity to the traction motors, common to older electric locos within the British sphere of influence. Diesel electric locomotives don't have them and they are often mistakenly thought to be a steering wheel owing to their nearly horizontal orientation to the floor. If the wheel is on a stand oriented perpendicular to the floor, it is most likely a hand brake as described above. If at any time the wheel becomes oriented below the engineer's normal operating position, then everyone involved is having a really bad day...

Just like everybody else, the "wheel" you saw was a handbrake, and most of the time the engineer does not even use it, mostly conductor's use it only. also, the following link will show you what the train driver controls look like, and are completely seperate from what you saw, there are wheels on the bottom of the train, and just follow wherever the tracks take them, that would be quite a challenge if the engineer had to steer the train since they work 12 hour days. http://www.railpictures.net/images/d1/8/9/9/8899.1202544000.jpg

That small wheel is a mechanical (as opposed to air) hand brake. Many switcher type (US) locomotives also had this wheel style hand brake in the cab. It is to be applied any time the Engineer leaves the locomotive as a safety measure. It's applied by turning it until it can't be turned any more, indicating the brake chain that that sets the brake shoes is tight. There is the wheel type manual brake and also the ratcheting lever type. All locomotives have this hand brake, or a "parking brake" in a sense. They're usually located outside the cab some where, but for some reason, the first few generations of switch locomotives had then in the cab. They must still be located in the cabs of commuter trains.

Even though the wheel is there, the train driver does not turn on curves - like a motor car. the train automatically takes a curve, as provided by the rails. Though the steering wheel is there, it is more or less a decorative purpose and in some cases, it is actually a hand brake.