A simple example of a LINQ query over a collection of objects (strings, in this case). helloLength1 and helloLenght2 are equivalent - the compiler just desugars the LINQ expression to the same AST that the second expression results in.

LinqToObjectsExample.cs

List<string> ss = new List<string>();
ss.Add("Hello");
ss.Add("World");

var helloLength1 = from s in ss
                   where s.StartsWith("H")
                   select s.Length;

var helloLength2 = ss.Where(s => s.StartsWith("H")).Select(s => s.Length);