First you need to setup your own content type. Go to your site url and add:

/admin/content/types/add

ex: http://www.planettutorial.com/admin/content/types/add

Enter in your Name (Blog), Type: (blog), and Description (This is your new blog post). You can leave the Title label and body label. Workflow, Leave at Published and Promoted to front page. Comment settings, because this is a blog, should be set to Read/Write.

Note: Make sure you setup proper permissions for your users to read and post comments.

I like to set the comments stuff to disable the comment subject field, preview is optional, and Display below post or comments.

Click "Save Content Type"

Next go to:

/admin/user/permissions

You'll want to look for comment module (again, make sure people can read and write). I let anonymous users read comments, but don't allow them to post (even without approval). There is just way to much spam.

If you have additional roles created for your site, like editor, you'll want to set the create blog content, delete blog content, and edit blog content for that role.

Next you'll want to create your first blog post. Go to Content Management -> Create Content -> Blog (/node/add/blog)

Enter your title, Body, you probably don't need to change input format. Lets keep it simple.

All your settings should be good, as we set them up earlier.

Click Save and your done!