const int led = 12;
const int btn = 10;

bool ledstate = false;
bool btnstate = 0;

void setup() {
 Serial.begin(115200);

 pinMode(btn, INPUT_PULLUP);

 pinMode(led, OUTPUT);

}

void loop() {
 btnstate = digitalRead(btn);
 if (btnstate == LOW && !ledstate){
  ledstate = true;
  digitalWrite(led, 1);
  delay(250);
}
else if(btnstate == LOW && ledstate){
  ledstate = false;
  digitalWrite(led, 0);
  delay(250);
}

}