Before we learn how to create a blog, you should have a domain and web hosting. You can read this article on how to create a website and then continue with this article.
Now you have a domain name and a web hosting account. You can login to your control panel (cPanel) and try to install WordPress software. WordPress is a software to create and manage a blog.
Most of the cpanel accounts have a one click wordpress installation feature. If your cpanel account does not have it, you can request your web hosting provider to install wordpress for you.
While installing wordpress, you have to set the username and password for the admin user. Once wordpress is installed, you can login to the admin section of your website using this url : www.yourwebsite.com/wp-login.php
Once you login to the wordpress admin section, you can go to Posts->Add New from the left menu and start writing your blog post. Just click Publish button once you have finished writing the post. Your blog post will immediately appear on your website.