I am just a learner in Drupal, Solr so can any one guide me how to implement indexing and how it is being updated in solr indexing whenever any updates being happened in Database so that in searching to get the recently posted also.
Start here: http://drupal.org/project/apachesolr
Also see http://19thstreetdesign.com/blog/2009.02.04/installing-apache-solr-drupal-6
Hey there.
Search Indexing in either standard Drupal search or apachesolr search works about the same way - every time that cron is run (http://www.example.com/cron.php), The search module looks for the next N items which are either new or updated and need to be re-indexed. (This N is set in the search settings at admin/settings/search for standard search or at admin/settings/apachesolr for the apache solr search.)
It's a good idea to take a few moments to look over both of those pages and see how the options are laid out - they're pretty well documented in the forms.
As for implementing indexing, you don't really have to - the modules take care of it for you. you just need to turn on search, and optionally install and turn on apachesolr, and it takes care of it for you.