Script that adds a projectile to the scene when the player presses the spacebar, and launches it in the direction the player is facing.

using UnityEngine;

public class ProjectileLaunch : MonoBehaviour
{
    public GameObject projectilePrefab;
    public float launchForce = 10f;

    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            GameObject go = Instantiate(projectilePrefab, transform.position, Quaternion.identity);
            Rigidbody rb = go.GetComponent<Rigidbody>();
            rb.AddForce(transform.forward * launchForce, ForceMode.Impulse);
        }
    }
}