what is the use of GroupBy in linq code example

Example 1: groupby in linq

var results = from p in persons
              group p.car by p.PersonId into g
              select new { PersonId = g.Key, Cars = g.ToList() };

Example 2: groupby in linq

//Method Syntax

        List<Result> results2 = persons
            .GroupBy(p => p.PersonId, 
                     (k, c) => new Result()
                             {
                                 PersonId = k,
                                 Cars = c.Select(cs => cs.car).ToList()
                             }
                    ).ToList();