These are the default steps that you need to do in order to add a blog post:
1. Go to Posts > Add New
2. Enter a title and some content.
3. Select a post category.
4. Add some relevant tags.
5. Add a featured image (should be 260 x 150 or 460 x 300 if you want to also support retina displays).
6. Insert all of your remaining content in the content area. You can have images, paragraphs, etc..
7. Write a few words excerpt (it is good for search results and SEO to have an excerpt, no matter what kind of content do you have in your post).
8. Hit “Publish” and you’re all done.