how do I enter vehicles

Pull the handle and get inside. Please, you must be more specific. What you want to do is make a collide around the door and give it a radius of however close you want the player to be to get in. Then use an OnTriggerEnter function to give you the option of pressing "E" or whatever you want to get in. Then use an OnTriggerStay funtion to get the the input of pressing E or whatever you want to get in. Then use an OnTriggerExit function to remove the option of getting in.