Wordpress is a very popular blogging tool. It is available as a free, hosted tool at - www.wordpress.com - or as a free, open-source version to download from www.wordpress.org and install on you own servers.

How to use Wordpress
Once you have set up an account on Wordpress and provided details of the name blog you want to write, management of your account and your blog(s) takes place via the dashboard. Here you can
  • edit your profile to provide information about yourself including a picture
  • edit your "about page"
  • customise the look and feel of your blog in terms of its appearance (view, select and even modify a theme) and add widgets
  • add and edit the links that appear in your blogroll
  • add other authors to your blog
  • manage your posts and the comments on your blog
  • access wordpress via your mobile: m.wordpress.com

Take a look at the Wordpress Manual, FLOSS Manual