Timer with a start and stop button

String timerStatus="off";boolean buttonValue1, buttonValue2;float startTime, endTime, eventTime;

void setup() { pinMode(2,INPUT); pinMode(4,INPUT); Serial.begin(9600);}
void loop() {
buttonValue1=digitalRead(2);buttonValue2=digitalRead(4);
if(buttonValue1==HIGH && timerStatus=="off"){ startTime=millis()/1000.0; //take clock time and convert to seconds if button1 is pushed and timer is off timerStatus="running"; //set timerStatus to "running" }

if(buttonValue2==HIGH && timerStatus=="running"){ endTime=millis()/1000.0; //take clock time and convert to seconds if button2 is pushed and timer is running timerStatus="off"; ////set timerStatus to "off: delay(500); }
eventTime=endTime-startTime; //time for event is endTime subtract startTime
Serial.print("The start time is ");Serial.print(startTime);Serial.print(" The end time is ");Serial.print(endTime);
if(eventTime>0){ Serial.print(" The event time is "); Serial.println(eventTime); }else{ Serial.println(" Waiting for event to finish "); }
}

What is millis()? How do I make a timer?

millis() is a function in Arduino that returns the running clock time on your Arduino since moment it was most recently turned on. It returns this time in milli seconds. Take that time and divide by 1000 and now you have seconds.

Any event can trigger your Arduino to record the time, not just a button.