How to create a form that allows user to enter a variable number of items
You need your answer to be an application - this is too broad.

I try to give basic idea.

You need one form which will be saved to the database each time a person fills the list.

It must contain 1 text box for Persons names. One List with all cars that are on the show and one empty list. And 2 buttons - cancel and save.

For each new person operator write his name of the person. Then operator selects cars from fisrt list and transfer its to the second. This can be done by double click or by selecting a car and pressing additional button. This must work in the opposite direction too.

Then when pressing save button the data will be saved inside database and the form will be reset - first list will contain all cars from the show, second will be empty and text box will be empty.

If operator presses cancel button the form will be reset without saving data to database.

You can try serach internet how to implement those lists in MS Access 2010.