Check out example codes for "fps camera unity". It will help you in understanding the concepts better.

Code Example 1

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
 
[AddComponentMenu("Camera-Control/Smooth Mouse Look")]
public class SmoothMouseLook : MonoBehaviour {
 
	public enum RotationAxes { MouseXAndY = 0, MouseX = 1, MouseY = 2 }
	public RotationAxes axes = RotationAxes.MouseXAndY;
	public float sensitivityX = 15F;
	public float sensitivityY = 15F;
 
	public float minimumX = -360F;
	public float maximumX = 360F;
 
	public float minimumY = -60F;
	public float maximumY = 60F;
 
	float rotationX = 0F;
	float rotationY = 0F;
 
	private List<float> rotArrayX = new List<float>();
	float rotAverageX = 0F;	
 
	private List<float> rotArrayY = new List<float>();
	float rotAverageY = 0F;
 
	public float frameCounter = 20;
 
	Quaternion originalRotation;
 
	void Update ()
	{
		if (axes == RotationAxes.MouseXAndY)
		{			
			rotAverageY = 0f;
			rotAverageX = 0f;
 
			rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
			rotationX += Input.GetAxis("Mouse X") * sensitivityX;
 
			rotArrayY.Add(rotationY);
			rotArrayX.Add(rotationX);
 
			if (rotArrayY.Count >= frameCounter) {
				rotArrayY.RemoveAt(0);
			}
			if (rotArrayX.Count >= frameCounter) {
				rotArrayX.RemoveAt(0);
			}
 
			for(int j = 0; j < rotArrayY.Count; j++) {
				rotAverageY += rotArrayY[j];
			}
			for(int i = 0; i < rotArrayX.Count; i++) {
				rotAverageX += rotArrayX[i];
			}
 
			rotAverageY /= rotArrayY.Count;
			rotAverageX /= rotArrayX.Count;
 
			rotAverageY = ClampAngle (rotAverageY, minimumY, maximumY);
			rotAverageX = ClampAngle (rotAverageX, minimumX, maximumX);
 
			Quaternion yQuaternion = Quaternion.AngleAxis (rotAverageY, Vector3.left);
			Quaternion xQuaternion = Quaternion.AngleAxis (rotAverageX, Vector3.up);
 
			transform.localRotation = originalRotation * xQuaternion * yQuaternion;
		}
		else if (axes == RotationAxes.MouseX)
		{			
			rotAverageX = 0f;
 
			rotationX += Input.GetAxis("Mouse X") * sensitivityX;
 
			rotArrayX.Add(rotationX);
 
			if (rotArrayX.Count >= frameCounter) {
				rotArrayX.RemoveAt(0);
			}
			for(int i = 0; i < rotArrayX.Count; i++) {
				rotAverageX += rotArrayX[i];
			}
			rotAverageX /= rotArrayX.Count;
 
			rotAverageX = ClampAngle (rotAverageX, minimumX, maximumX);
 
			Quaternion xQuaternion = Quaternion.AngleAxis (rotAverageX, Vector3.up);
			transform.localRotation = originalRotation * xQuaternion;			
		}
		else
		{			
			rotAverageY = 0f;
 
			rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
 
			rotArrayY.Add(rotationY);
 
			if (rotArrayY.Count >= frameCounter) {
				rotArrayY.RemoveAt(0);
			}
			for(int j = 0; j < rotArrayY.Count; j++) {
				rotAverageY += rotArrayY[j];
			}
			rotAverageY /= rotArrayY.Count;
 
			rotAverageY = ClampAngle (rotAverageY, minimumY, maximumY);
 
			Quaternion yQuaternion = Quaternion.AngleAxis (rotAverageY, Vector3.left);
			transform.localRotation = originalRotation * yQuaternion;
		}
	}
 
	void Start ()
	{		
                Rigidbody rb = GetComponent<Rigidbody>();	
		if (rb)
			rb.freezeRotation = true;
		originalRotation = transform.localRotation;
	}
 
	public static float ClampAngle (float angle, float min, float max)
	{
		angle = angle % 360;
		if ((angle >= -360F) && (angle <= 360F)) {
			if (angle < -360F) {
				angle += 360F;
			}
			if (angle > 360F) {
				angle -= 360F;
			}			
		}
		return Mathf.Clamp (angle, min, max);
	}
}

Code Example 2

//Fixed the issues with the previous controller
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CameraLook : MonoBehaviour
{
	public float minX = -60f;
	public float maxX = 60f;

	public float sensitivity;
	public Camera cam;

	float rotY = 0f;
	float rotX = 0f;

	void Start()
	{
		Cursor.lockState = CursorLockMode.Locked;
		Cursor.visible = false;
	}

    void Update()
    {
		rotY += Input.GetAxis("Mouse X") * sensitivity;
		rotX += Input.GetAxis("Mouse Y") * sensitivity;

		rotX = Mathf.Clamp(rotX, minX, maxX);

		transform.localEulerAngles = new Vector3(0, rotY, 0);
		cam.transform.localEulerAngles = new Vector3(-rotX, rotY, 0);

		if (Input.GetKeyDown(KeyCode.Escape))
		{
        	//Mistake happened here vvvv
			Cursor.lockState = CursorLockMode.None;
			Cursor.visible = true;
		}

		if (Cursor.visible && Input.GetMouseButtonDown(1))
		{
			Cursor.lockState = CursorLockMode.Locked;
			Cursor.visible = false;
		}
	}
}

Code Example 3

public float turnSpeed = 4.0f;
public float moveSpeed = 2.0f;
 
public float minTurnAngle = -90.0f;
public float maxTurnAngle = 90.0f;
private float rotX;
 
void Update ()
{
    MouseAiming();
    KeyboardMovement();
}
 
void MouseAiming ()
{
    // get the mouse inputs
    float y = Input.GetAxis("Mouse X") * turnSpeed;
    rotX += Input.GetAxis("Mouse Y") * turnSpeed;
 
    // clamp the vertical rotation
    rotX = Mathf.Clamp(rotX, minTurnAngle, maxTurnAngle);
 
    // rotate the camera
    transform.eulerAngles = new Vector3(-rotX, transform.eulerAngles.y + y, 0);
}
 
void KeyboardMovement ()
{
    Vector3 dir = new Vector3(0, 0, 0);
 
    dir.x = Input.GetAxis("Horizontal");
    dir.z = Input.GetAxis("Vertical");
 
    transform.Translate(dir * moveSpeed * Time.deltaTime);
}

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