trying to make my own emit particles

so i have this project due for school were we’re learning unity but I’m having a heck of a time trying to implement a particle system. i tried making a class that would control the attributes, then spawn a game object in update so the particles will keep coming out, then afterwords was gonna add gravity and start detecting collisions but I haven’t even gotten to that part yet. And for this i can’t use the particle emitter or rigid bodies.

heres what i’ve most recently been working with, it seems to spawn one every second but i can’t move them for the life of me and i feel like something is fundamentally wrong with how I’m going about this.

using UnityEngine;
using System.Collections;

public class particle : MonoBehaviour {
	public float age = 2;
	public float ageMax = 6;
	public Vector3 velocity;
	public Vector3 position = new Vector3(0,6,0);
	public float mass = 1;

	void Start() {
		
	}

	}
public float lastSpawn=0;

	void Update() {

		
		if (Time.time > lastSpawn + 1.0) {
			GameObject particley = GameObject.CreatePrimitive (PrimitiveType.Sphere);
			particley.transform.localScale = new Vector3(0.2f,0.2f,0.2f);
			particley.transform.position = new Vector3(0,4.5f,0);
			lastSpawn = Time.time;
			float grav = 20;
			float i;
			bool die = false;
			for (i = 0;i < 20; i++) {
				velocity.x = Random.Range(0,3);
				velocity.y = Random.Range(0,3);
				velocity.z = Random.Range(0,3);
				if (i == 19) {
					die = true;
				}
			}
 	
			if (die == true) {
				Destroy(particley);	
				die = false;
			}
		
			
		}
	}
}

I’m putting this script on a cube that will act like its just forever pouring little spheres out of it, eventually I would add some side direction to it so they go back and forth. Also i’ve tried just doing a constant translate down on particley but that didn’t work either. Any feedback is appreciated before i pull my hair out over this, thanks!

any feedback would be great, even how I should design it. I’ve been thinking maybe go with just a class with all it’s properties, a creator function and play with those

Your for loop goes up to 20 and when i is 19 you destroy the “particle” you just created - so you’re creating it and destroying it in the same frame.