How to associate prefab with a variable in C#?

I’m following this tutorial to make a simple FPS except I do the code in C#.
It says to instantiate a missile (rigid body sphere) I need to associate the Missile prefab with projectile variable and when the code is in JS it can be done by dragging and dropping since I see all the information about the script in the Inspector section. When it’s C# Inspector only shows that my script is attached to the Launcher, no variables and all.
How do I associate Missile prefab with projectile variable?

Just in case, here’s my code:

using UnityEngine;
using System.Collections;

public class MissileLauncher : MonoBehaviour {

	Rigidbody projectile; 
	int speed= 20; 
	
	void  Update (){ 
		
 		if(Input.GetButtonDown("Fire1"))
  			{ Rigidbody instantiatedProjectile=(Rigidbody)Instantiate
				(projectile,transform.position,transform.rotation); 
  			  instantiatedProjectile.velocity=transform.TransformDirection(new Vector3(0,0,speed)); 
				
  			  Physics.IgnoreCollision(instantiatedProjectile.collider,transform.root.collider); 
 	 		}
		
}
}

Make it a public variable.

C#-scripts only show public variables in the inspector. If you don’t put public/private in front of a variable, it is private by default.