How to make dialogue in Unity3D?

I am a begginer of Unity3D, I have poor knowledge of programming.

I create a plane in the scene, named it with "HumanA".Then I want that result: When a player in the Game click on HumanA, GUI appears like dialogue in Game, the dialogue is divided into three parts and automatically play. How can I do in Unity3D? What should I write in JavaScript or C script? Thanks!

Since you lack programming knowledge, you may want to consider the Unity Dialog Engine. As it includes source (which I haven't seen myself) it might work as a learning tool too.

Just put up a Dialogue Generator released under CC: