Buttons used to Calibrate A System URGENT HELP NEEDED

We are trying to use a button to calibrate our system. We are new to using Arduino. We have an LCD hooked up that is already connected in to the system. We want the button to be pushed, then we want the screen to say, "To Calibrate System, Press Button Again". Then when the button is pressed again, we want the Arduino to store the value off of the Analog 0 (A0). If anybody could help us with this it will be greatly appreciated! (The button is connected on the Digital 5 pin)

Do you have any code created yet?
Use the code tags button (#, above) and post your code between the tags.

This is what we have so far. We have the analog monitoring a amperage. And we want the button to be pushed and go through the prompt to calibrate. Then that calibrated number will be the number that is placed where the 225 is and from there we program the subtraction for it. We just need help getting the button to calibrate.

#include <LiquidCrystal.h>

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
void setup(){

  lcd.begin(20, 4);

  pinMode(5, OUTPUT);    //this is the button

  pinMode(4, OUTPUT);    //this is the green led
  digitalWrite(4, LOW);
  pinMode(3, OUTPUT);    //this is the yellow led
  digitalWrite(3, LOW);
  pinMode(2, OUTPUT);    //this is the red led
  digitalWrite(2, LOW);

void loop()
  int sensorValue = analogRead(A0);
  lcd.setCursor(0, 2);

  if(sensorValue >= 225){
 digitalWrite(4, HIGH);
  digitalWrite(3, LOW);
  digitalWrite(2, LOW); 
}else if(sensorValue <= 224 && sensorValue >= 217){
 digitalWrite(4, LOW);
  digitalWrite(3, HIGH);
  digitalWrite(2, LOW); 
  }else if(sensorValue <= 216 && sensorValue >=101){
 digitalWrite(4, LOW);
  digitalWrite(3, LOW);
  digitalWrite(2, HIGH); 
   }else if(sensorValue <= 100){
 digitalWrite(4, LOW);
  digitalWrite(3, LOW);
  digitalWrite(2, LOW); 
 lcd.setCursor(0, 0);
 lcd.print("ACSavers Air Filter");
lcd.setCursor(0, 1);
lcd.print("Notification Device");
int sensorValue2 = analogRead(A0);
float calculatedsensorValue = sensorValue2 / 250.0 ;
lcd.setCursor(0, 3);