make objects slowly go up, then slam down

Well you weren't too specific, so I'll just give you a basic tutorial on transform.Translate, in C-sharp, since you also didn't specify the language you want to use. This will still get you going.

 using UnityEngine;
 using System.Collections;
 
 public class Example : MonoBehaviour
 {
     float speed;
     Vector3 direction;
     float min;
     float max;
     float units = 2.0f;
 
     void Start()
     {
         //Set max to CURRENT position on Y axis, and set min to current minus units (2.0 in this example).
         max = transform.position.y;
         min = transform.position.y - units;
         
         //Set first direction to be down
         direction = Vector3.down;
     }
 
     void Update()
     {
         //Change speed depending on direction of object translation.
         if(direction == Vector3.down)
         {
             speed = 10.0f;
         }
         
         else if(direction == Vector3.up)
         {
             speed = 1.0f;
         }
         
         
         
         
         //Use transform.Translate to move the current direction and current speed.
         transform.Translate(direction * speed * Time.deltaTime);
         
         
         
         
         //Change direction if object has reached min or max position on the Y axis (up and down).
         if(transform.position.y >= max)
         {
             direction = Vector3.down;
         }
         
         if(transform.position.y <= min)
         {
             direction = Vector3.up;    
         }
     }
 }