How do I use a servo in an interrupt? I am working on a small circuit now where I increment the rotation of a servo motor and at the same time blink a LED.

I have used all methods I know to do it but still it does not work or it blinks and then the servo start working but never both at the same time.
This is what i am basically working with:

  for(position=0;position&lt;=90;position=position+5){
    digitalWrite(led_pin,HIGH);
    delay(200);
    digitalWrite(led_pin,LOW);
    delay(200);
    servoBar.write(position);
    delay(15);
  }


But it blinks once and then it stops and the servo start working right after that.

I know I must not use delays in interrupts. I am using a function that I can but just to show you what I am working with.
The problem is that the delay routine is blocking. It stops operation and blocks other things from happening. Have a look at the Blink without delay example in the example tab. (also linked below)
https://www.arduino.cc/en/Tutorial/BlinkWithoutDelay

What you need to do is to not block. Call the time checker often and check if the time you want delayed has run out. The perform the action needed to be done at that time. 

This is a more sophisticated way to deal with timed events. Also look at this
Demonstration code for several things at the same time.
https://forum.arduino.cc/index.php?topic=223286.0

Have fun learning. :)