Anchors are about finding matches beginning with or ending with a certain pattern.

This example from an irb session helps to show what \b, \w, ^, $ and \B do. \b - matches a word boundary, \w - matches a word character, ^ - matches a character at the beginning of a line, $ - matches the character at the end of a line, and \B matches a word boundary charcter which does not match \w.

irb(main):010:0> "paella"[/\ba/]
=> nil
irb(main):013:0> "artistic paella wake"[/\wa/]
=> "pa"
irb(main):026:0> "artistic paella wake"[/\B.[a-z]a$/]
=> nil
irb(main):027:0> "artistic paella wake"[/\B.[a-z]$/]
=> "ke"
irb(main):039:0> "artistic paella wake"[/\B./]
=> "r"
irb(main):040:0> "artistic paella wake"[/\Ba./]
=> "ae"
irb(main):044:0> "artistic paella wake"[/[^\B.{3}]/]
=> "a"
irb(main):046:0> "artistic paella wake"[/[^\B.]{3}/]
=> "art"
irb(main):047:0> "artistic paella wake"[/[^\w]{3}/]
=> nil
irb(main):047:0> "artistic paella wake"[/[^\w]{3}/]
=> nil
irb(main):048:0> "artistic paella wake"[/[^\br]{3}/]
=> "tis"
irb(main):050:0> "artistic paella wake"[/[^\b]{3}/]
=> "art"
irb(main):051:0> "artistic paella wake"[/[^\ba]{3}/]
=> "rti"
irb(main):054:0> "artistic paella wake"[/\ba/]
=> "a"
irb(main):055:0> "artistic paella wake"[/\ba./]
=> "ar"
irb(main):058:0> "people paella wake"[/\bp./]
=> "pe"
irb(main):060:0> "apostrophe paella wake"[/\bpa./]
=> "pae"
irb(main):061:0> "apostrophe paella wake"[/\bp./]
=> "pa"
irb(main):062:0> "apostrophe paella wake"[/\Bp./]
=> "po"
irb(main):064:0> "pancake paella wake"[/\Bp./]
=> nil
irb(main):065:0> "anticipated paella wake"[/\Bp./]
=> "pa"
irb(main):066:0> "anticipated paella wake"[/\Bp../]
=> "pat"
irb(main):067:0> "anticipated paella wake"[/\wp../]
=> "ipat"