How do i use functions in my project?

im designing a bus ticket program which has to display ticket information like total passengers,total cost etc,stop number and address

This is what i have done so far.

/* Bus Ticket program. A program which could be used to issue bus tickets.*/
/*Program by Neil Currie*/
/*BTEC NATONAL DIPLOMA COMPUTING AND I.T.*/

#include <conio.h>
#include <stdio.h>
#include <ctype.h>

#define TRUE 1
#define FALSE !(TRUE)

void main ()
{
char getstop;
int done;

clrscr();
gotoxy(30, 5);
printf("*******************");
gotoxy(30,6);
printf("Welcome to BromBus");
gotoxy(30,7);
printf("*******************");

gotoxy(5,10);
printf("Please select your bus stop number. \n");
printf("1 - Tesco.\n");

printf("= - Selection made:\n");

done=FALSE;
while(!done)
{
getstop=toupper(getch());
switch(getstop)
{
case '1':
printf("You have selected to travel to Tesco\n");
break;

case '=':
done=TRUE;
}
}
}

at the moment when a number 1 is typed it displays "you want to travel to tesco"

Do i need to get the answer to be assigned to a variable ? if so how?

whats the next stage in my program?

i need to use at least 3 functions but im not sure how to use functions and what to use as function for in this program.

and i have to display a summary of the ticket information for 15 seconds.

can anyone help please ?