Hi guys, I am a noob into this, i have some doubts on modeling 1. while modeling a car should i go ahead and model a low poly model and then a high poly or should i go ahead model a high poly and then reduce it down to a low poly model 2. I am have thought bout an idea for a game so i wanna put it together and wanna start modeling a level for it wanted to know procedure on how to go bout it.

There are tools that can generate optimized low poly models with a normal map from high poly models.
They're experimental, of course, but still worth looking into.

While what loufoque says is true, they simply don't get you the results you want.

Model the car for real-time use, import into a sculpter to make a high poly version, and then export a normal map and apply it to the real-time version. Tried and true. [wink]

As for the level design question, that varies wildly based on the game engine you're using.