Sample Player.cs without comments.

PlayerUnCommented.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Player : MonoBehaviour
{
    [SerializeField] private Vector3 startPos;
    private Vector3 playerPos;
    private Vector3 screenPos;
    [SerializeField] private float speed;
    [SerializeField] private float upperLimit;
    [SerializeField] private float widthLimit;
    private float currentSpeed;
    [SerializeField] private SpriteRenderer currentThruster;
    [SerializeField] private Sprite[] thrusters;
    [SerializeField] private Projectile currentProjectile;
    [SerializeField] private Transform[] projectileLocations;
    private float fireTimePassed;


    void Start()
    {
        startPos = transform.position;
        currentSpeed = speed;
    }

    void Update()
    {
        screenPos = Camera.main.WorldToScreenPoint(transform.position);

        Movement();
        Fire();
    }

    private void Movement()
    {
        playerPos = new Vector3(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
        transform.Translate(playerPos * Time.deltaTime * currentSpeed);
        
        if (transform.position.y > upperLimit)
        {
            transform.position = new Vector3(transform.position.x, upperLimit);
        }
        else if (transform.position.y < 0.5f)
        {
            transform.position = new Vector3(transform.position.x, 0.5f);
        }

        if (screenPos.x < 0f - (transform.position.x * widthLimit))
        {
            if (playerPos.x > 0)
            {
                currentSpeed = speed;
            }
            else
            {
                currentSpeed = 0f;
            }
        }
        else if (screenPos.x > Screen.width - (transform.position.x * widthLimit))
        {
            if (playerPos.x < 0)
            {
                currentSpeed = speed;
            }
            else
            {
                currentSpeed = 0f;
            }
        }
        
        if (currentThruster.sprite == thrusters[0])
        {
            currentThruster.sprite = thrusters[1];
        }
        else
        {
            currentThruster.sprite = thrusters[0];
        }
    }

    private void Fire()
    {
        fireTimePassed += Time.deltaTime;
        
        if (Input.GetMouseButton(0) && fireTimePassed >= currentProjectile.FireDelay)
        {
            foreach (var location in projectileLocations)
            {
                GameObject tempProjectile = Instantiate(currentProjectile.gameObject, location.position, Quaternion.identity);
            }

            fireTimePassed = 0f;
        }
    }

}