Crouching Help!

(This is in C#)
Here is the code:

public void Start () 
{
	controller = GetComponent<CharacterController>();
	mainCamera = gameObject.tag("MainCamera");
	standardHeight = controller.height;
	crouchHeight = controller.height/2;
	crouching = false;
}

And Unity gives me this error:
The member `UnityEngine.GameObject.tag’ cannot be used as method or delegate

So what do I need to do?

The error is telling you that you are taking a variable (here: “tag” ) and tell it to DO something (by adding round brackets behind it); but a variable can never do anything so unity doesn’t know what you are trying to do… And neither do I

mainCamera = gameObject.tag("MainCamera");

Are you trying to assign the Tag ‘MainCamera’ to the variable ‘mainCamera’? (Not sure, if that’s even possible…)
Or are you trying to assign the Object that has the Tag ‘MainCamera’ to the variable ‘mainCamera’? (I assume you want this.)
You need to do

mainCamera = GameObject.FindWithTag("MainCamera");