NullReferenceException: Object reference not set to an instance of an object HELP

im new to unity (no need to welcome)i learned already,but the only thing i cant stand is the NullReferenceException: Object reference not set to an instance of an object

here is the full error:
NullReferenceException: Object reference not set to an instance of an object
ThirdPersonController.UpdateSmoothedMovementDirection () (at Assets/Standard Assets/Character Controllers/Sources/Scripts/ThirdPersonController.js:129)
ThirdPersonController.Update () (at Assets/Standard Assets/Character Controllers/Sources/Scripts/ThirdPersonController.js:302)

im not good with errors,what im trying to do is make the character mmove,some said the camera but i made a camera and added,BUT HALP please

The error is telling you that there is a problem at lines 129 of ThirdPersonController. If we crack open the script and look at that line we see a reference to the the Camera.main. Camera.main is a static variable that is set when a Camera is given the MainCamera tag. You can see that in the image below. There is probably not a camera in your scene with the MainCamera tag, so that means that the Camera.main variable is never set and you get a NullReferenceException

alt text.