unity3d - Create random falling objects in unity C# -

i starting learn unity3d , developing 2d game need @ main menu. have coin texture spawn multiple times above screen , fall down create falling coin texture. spawn points should random , entities should destroyed after falling off screen, have no idea how it. appreciated. thank

image upload: http://imgur.com/ol4vkr2

i give starting points done task. can read about`

1. rigidbody(rigidbody2d)
2. collider(collider2d)
3. monobehaviour callbacks example ontriggerenter(ontriggerenter2d) or oncollisionenter(oncollisionenter2d)
4. for randomness can read random class , methods random.randominsideunitcircle.