I don't know how to put a trial on a vehicle, i don't have a script, can someone please send me a link to a video or something?
ROBLOX actually has a class built into it for trails and requires no Lua programming!
You can read about it here: Link
Here's an example of me using it:
Those green points are "attachments" that you have to place onto the entity itself. After doing so specify the attachment in the Trail's properties.