Lambda expressions with List in C#

Question

Please consider this example,
 
List lst = new List { 1, 2, 3, 4 };
int result = lst.Aggregate((x, y) => x * y);
 

As per the articles (x,y) specifies input parameters and x*y as implementation, my doubt is, aggregate() is the method of list, then it has to have inner implementation of aggregation by its own, then what (x*y) specifies or rather needed here...
 
Please mention the articles explaining lambda and list separately...
 
Thanks in advance,