Irb loaded constants

…When irb loads it somehow initializes all kinds of cool constants
like $:, $LOAD_PATH, $LOADED-FEATURES ETC…where could i get info on
all of these things…the picaxe has some $… but not all $ENGLISH
stuff…and to all thanks for answering my previous question ‘cannot
require ‘date’ in irb’…it was already required when i looked into
$LOADED-FEATURES…because my rubyopt=rubygems and thats oka…