am newbie in wordpress.. I have installed its version 3.1.1..
I just want to know how can I make the post password protected and how to add excerpt for it....?
Assuming you mean WordPress 3.1.1, then the answer is that on the page where you author a post there is a place to enter an excerpt. You can read more in the WordPress codex here: http://codex.wordpress.org/Excerpt
Regarding password protection, you can make a post password protected or private (different things). In a standard WP installation there is a "Publish" panel near the top right of the page that controls this. Here is the documentation: http://codex.wordpress.org/Content_Visibility
More sophisticated password protection options are available via plugins.