Please suggest, which open sources content management system is good to create library website or portal?
Joomla is pretty good to design any handsome website.
Hope this help.
The two most common open source platform for developing a website is WordPress and Joomla. WordPress is quiet easy and simple and the most used CMS over the world where as Joomla is slight complicated but more dynamic.
Again if you are thinking of free website then WordPress is the best option. Google Sites can also help you out for the same (not open source). If you are thinking it with a purchase domain then several hosting sites will provide you a storage space with some minimal charges.
To develop your site with WordPress/Joomla you can take help from Here
There are many CMS to design websites / portals, you need to decide where your expertise lies on.
Wordpress, Drupal, Joomla are the popular ones.
I would vote for Wordpress, since it has great themes and plugins as options (both free and paid ones), as well as friendly User Interface.