Check out example codes for "how to get component in unity c#". It will help you in understanding the concepts better.

Code Example 1

GetComponent<Rigidbody>(); //used to find component on character (rigid body can be changed)
GameObject.FindGameObjectWithTag("player"); //finds any game object in the scene with this tag

Code Example 2

rb = GetComponent<Rigidbody>();

Code Example 3

//First script 
public class Enemy : MonoBehaviour{
  public int health = 10;
  public void saySomething(){
    Debug.Log("Hi, i am an enemy.");
//Second script
//There is one thing though,
//if the script is located on another gameobject,
//which will be most likely, you have to somehow
//find that gameobject first. There are many ways of
//doing it, via raycast, collision,
//trigger, find by tag, find by gameobject etc.
//But i will use the simplest way to understand,
//that is declaring public GameObject in player script,
//which contains Enemy, and later you just drag and drop the
//gameobject in the inspector.
public class Player : MonoBehaviour{
  //Drag and drop gameobject with script Enemy in inspector
  GameObject enemyGameObject;
  void Start(){       
    //We get Enemy component - script
    //from public gameobject which contains this script
    Enemy enemyScript = enemyGameObject.GetComponent<Enemy>();
    //This will debug Enemy health is: 10  
    Debug.Log("Enemy health is:"+  
      //This will debug "Hi, i am an enemy." 

Code Example 4

public GameObject Var; //only if the component you want is on a different gameObject

void Start(){
	Var.GetComponent<Component>(); //just GetComponent<Component>(); if the component you want is on the same object as script

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