A blog is Joomla's out-of-the-box built-in capability. If you need a blog, installing Joomla is all you need to do.
Create your blog categories.
Then go to Content > Articles > Add New Article and begin creating your blog posts.
Once you are ready to publish your blog posts, you simply point the Home menu item to your blog category.
Now your site visitors will see your blog posts listed in chronological order. Your blog is ready.
This is exactly how we built our own blog here at Joomlashack.