Now when I allow self-registration, why the user can't see the blog posts ? I have checked the post is not private or anything. its the default post when we install blog engine ?

In the setting or rights of role "anonymous", it is  enabled "View public posts"

so i am assuming person who registers is considered as anonymous ?

In my "Initial Role for self registration" is set to none: Select

Since I have not set it so i am assuming it is considering the self registered user as anonymous ? if no then, why anonymous role is not visible in the drop down menu for "Initial Role for self registration" ?

Please clarify

Anonymous is a reserved role for unregistered users. You should create a new role, for example "Registered" or "Reader" or whatever and it will show up in "initial role" drop down. You can model it after anonymous, so it will pick up same rights, if you want to.

thank you