Check out example codes for "top down shooting in unity 2D". It will help you in understanding the concepts better.

Code Example 1

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

public class Shooting : MonoBehaviour
{

    public Transform firePoint;
    public GameObject bulletPrefab;

    public float bulletForce = 20f;

    // Update is called once per frame
    void Update()
    {
        if(Input.GetButtonDown("Fire1"))
        {
            Shoot();
        }
    }  

    void Shoot()
    {
        GameObject bullet = Instantiate(bulletPrefab, firePoint.position, firePoint.rotation);
        Rigidbody2D rb = bullet.GetComponent<Rigidbody2D>();
        rb.AddForce(firePoint.up * bulletForce, ForceMode2D.Impulse);
    }

}

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