Please Help !

Hey Guys i wanna know how levels are build in unity . i mean i am making a game that have different things to unlock like locations/cars etc . so if the user clicks on a particular location it should start a game on that location with the specified car ...

i have no clue how to do this . can you guys guide me to a document/tutorial which explains this or can you just explain it here .

Thanks in advance and try not to be rude :P :)