Question About Generic Lists

 Hi,
 I have a quick question about using generic lists.
Say I create a generic list of type "car":
private List<car> _cars= new List<car>();
Then I add some values to it like [honda,red,1999], [ford,green,2008], etc....
 
Now I know the developer can search through the list by using the index, like _cars[1] = [ford,green,2008]
But I also noticed that some classes I've seen allow you to use an additional key in the bracket.... like _cars["ford"]  = [ford,green,2008]
 
How do I design a generic list that accepts a string as the key like above?

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