Screen Output and Keyboard Input

I suppose the first question should be "can I use Arduino as simple C compiler?". How do I execute the code from sketch board? Thanks in advance for advice.

I tried to print out "Hello World" as my 2nd program in learning how to use Arduino. I have tried an example to upload the program to make the LED blink.

Can Serial Monitor be my output on code executed on Arduino Uno? If yes, could keyboard be my input as USB is bi-directional?

I was just getting to know Arduino environment.

Can Serial Monitor be my output on code executed on Arduino Uno?

Yes.

If yes, could keyboard be my input as USB is bi-directional?

Not directly. The keyboard is not directly connected to the Arduino or serial port. The active application gets keyboard data. If that is the Serial Monitor, the Serial Monitor can send the keystrokes to the Arduino, but only when the Send button is pressed.

Could I use a dumb terminal (HyperTerminal or ProComm) as Arduino hardware peripheral? Why is Arduino serial monitor requiring "SEND" to send keystrokes?

Why is Arduino serial monitor requiring "SEND" to send keystrokes?

Because that's what the people that wrote it wanted. If you don't like that, you are free to use something else/write your own.

Could I use a dumb terminal (HyperTerminal or ProComm) as Arduino hardware peripheral?

How can you use software as a hardware peripheral?

I suppose peripheral may not a right word. I meant to say the following link:

PC with ProComm - USB cable - Arduino Uno

Does anyone have some example of code that can say "Hello World." to serial monitor in Arduino software?

Yes, you can use hyperterm (or similar terminal emulator) as an I/O device for your Arduino.

Does anyone have some example of code that can say "Hello World." to serial monitor in Arduino software?

void loop () {}

void setup ()
{
  Serial.begin (9600);
  Serial.println ("Hello world.");
}

(uncompiled, untested)