When my car crashes into the guards, the game is supposed to be over!

Hey guys!

So, this is probably a very stupid question to ask. But I am new to unity, and I really need help...fast!!

So I am making a car game and I am using the car game tutorial made by Unity. But I want my game to start with a movieclip I have made, and when the car crashes into the guards on the side of the road, I want the Game to end, and a new movie clip to appear. This is the most important part! Then, I would love it if you could tell me how to create a "try again" button.....I'm really stuck guys, so I would really appreciate it if you would take te time to help me :) :) :)