How i make a video to play,when the player starts the game?
You could use a movie texture if you’re talking about importing a video file into Unity.
If you’re video is something in the game you’re making then I (personally) would just make a level and model/code the animation.
http://docs.unity3d.com/Documentation/Manual/VideoFiles.html
Or, if you don’t have pro and don’t care about app size, fake it with a GUITexture you change the texture of every frame.
Or, search for plugins.