OrderBy, ThenBy, GroupBy

Ordering

var words = new[] { "pear", "fig", "apple" };
var sorted = words.OrderBy(w => w.Length).ThenBy(w => w);
// fig(3), apple(5), pear(4)? no: fig, apple, pear sorted by length: fig, pear, apple

OrderBy(key) sorts ascending by the key; OrderByDescending flips it. ThenBy breaks ties: first by Length, equals sorted alphabetically. Replace, don't re-order: calling OrderBy twice replaces the first ordering — the second call's keys become primary. Chains read: primary, then tie-breakers.

Grouping

var byLength = words.GroupBy(w => w.Length);
foreach (var g in byLength)
{
    Console.WriteLine($"length {g.Key}: {string.Join(",", g)}");
}
// length 3: pear,fig — no: 3: fig  5: apple,pear

GroupBy(key) yields a sequence of groups, each with a Key and the elements sharing it — a Dictionary in fluent form. Group order is encounter order; element order within a group is source order.