Can I show email Id entered by user to the visitors? Suppose When a user doing the registration, site will ask that "Do you like to show your email ID?" If the user selects YES then the site will show his email ID and if it selecet no the site will not, I am new to the drupal, so please help me.
Check out the following modules
User Field Privacy

A successor of Profile Privacy for Drupal 7 that works with standard Field API (ie. non-profile) user fields.
In easier-to-understand terms:

All the user fields should have an &quot;alterable privacy&quot; checkbox.
If this checkbox is ticked, the user should be presented with an
additional checkbox for the privacy-enabled fields on user edit forms
to be able to make that fields' values private.
If this second checkbox is ticked for a field of a user, only the
site administrators (members of roles with the &quot;Access private
fields&quot; permission) and the user herself should be able to view that
field's value.


Profile Privacy

This module allows users to set privacy options for their profile fields when using the core profile.module. It does not create any settings pages or configuration screens, and it integrates seamlessly with the existing profile module.