How do you use datastore for parts.?

-- Define Datastore

local PlayerCars = {}

Datastore = 

game["Players"].PlayerRemoving:connect(function(Player)
    Datastore:SetAsync(Player.userId,unpack(PlayerCars))
end)

I'd say go to data persistence if you want the easier method for that.

http://wiki.roblox.com/index.php?title=Data_store

*Unlike Data Persistance, Data Stores cannot save ROBLOX instances directly. For example, calling DataStore:SetAsync("key", Instance.new("Part")) will throw an error. You should write a function that converts the instance to a table or string. *

So for what you would do for datastores, is make each part of the car converted into a string(So you'll have to make a script that reads that string and creates the brick for X car).