Here is your first c program. Write carefully because C Language is a case sensative language. 

#include < stdio.h>
void main()

{
    printf("Hello World\n");
}

Press ALT+F9 to compile your program. If you have any error in your program, you will get the message, remove your errors and then execute your program you will got the out put.

Hello World

printf()
The printf() function prints output to stdout, according to format and other arguments passed to printf(). The string format consists of two types of items - characters that will be printed to the screen, and format commands that define how the other arguments to printf() are displayed. 

 printf( "Hello World’ );

scanf()
The scanf() function reads input from stdin, according to the given format, and stores the data in the other arguments. It works a lot like printf(). The format string consists of control characters, whitespace characters, and non-whitespace characters.

void main(void)
{
int i;
scanf(“%d”,&i);
printf(“%d”,i);
}