I agree with Trev; it would take a very long time to explain the whole thing.
Your question is a little too broad as well. Are you wanting an electrical-type explosion like those featured in District 9? Are you wanting a fiery explosion such as in X-Men 2? Is it supposed to be the car’s gasoline exploding or are you wanting a more realistic explosion where the car blows apart without so much fire? What’s causing the explosion? What kind of camera shot were you hoping to achieve?
The simplest thing for almost every effect is to do it practically. Try to get your hands on a scale model to blow up. (If you have access to a camera that does over-cranking or “smooth slo-mo” than that’s perfect.)
If you don’t have the ability to fake it with a real explosion on a model here are a couple things off the top of my head:
It’s easier if you don’t move the camera or the car. Get pictures of the car from different angles.
Crumple the pieces as per Andrew Kramer’s tutorial and make them fly away composited with whatever type of explosion you’re using. You can use pieces of explosion (and added dust hits/debris/etc.) to hide problems.
Stock footage (like this) gets you the most realistic-looking explosions, however you can create them with ParticleIllusion (it has free emitters already built with tons of different types of explosions) or any After Effects particle plug-in. However, if you’re creating one from scratch in Particular or something be prepared to either spend a lot of time on it or have it look horribly fake.
In all actuality doing this digitally at all is going to look really fake unless you spend a lot of time on it.
Don’t forget: if your explosion is the Hollywood fiery kind, to create light on the ground and in any reflective surface nearby. Andrew Kramer has a tutorial on that as well.
Actually, you should probably look through all of Andrew’s tutorials. You’ll probably be inspired to add some things to your film just from reading through his stuff.
If you have any further/more specific questions, feel free to post them.
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