Code check:
This is offtopic here but the people over at CodeReview are more than happy to help you.
I strongly suggest you to do so, there are several things that need attention in your code. Likewise I suggest that you do start reading tutorials since there is really no good reason not to do so.
Lists:
As you said yourself: you need a list of items. The way it is now you only store a reference to one item. Lucky there is exactly that to hold a group of related objects: a List.
Lists are very straightforward to use but take a look at the related documentation anyway.
A very simple example to keep multiple bikes in a list:
List<Motorbike> bikes = new List<Motorbike>();
bikes.add(new Bike { make = "Honda", color = "brown" });
bikes.add(new Bike { make = "Vroom", color = "red" });
And to iterate over the list you can use the foreach statement:
foreach(var bike in bikes) {
Console.WriteLine(bike.make);
}