First of all, after you click "POST," you will see a "Title" box and a large box which says "Write your story ..."

At the TOP-RIGHT of that large typing box, you will see either "Editor" or "Markdown."

If you want to edit or format your text, click on “Editor,” and the Editorial icons will appear. (If you want to use those editorial functions, you must click on "Editor" before you type any of your text. Because as soon as you insert even one letter, the "Editor" option disappears.)

After clicking on "Editor," input all your text and format it to your satisfaction. (There is a "preview" screen below the typing box.)

If you want to insert images or links. ... After you have inserted and formatted all your text, then go to the "Raw HTML" at the TOP-RIGHT of the large typing box (where it had previously said "Editor" or "Markdown"). Click on "Raw HTML, and then you can insert all the images (by copy and paste, or drag and drop) and any links.

Also, here are a few links that might help for certain tasks.
https://steemit.com/steemit-help/@krnel/how-to-align-images-in-steemit-posts-left-right-and-center

http://markdownpad.com/

https://guides.github.com/features/mastering-markdown/#intro

Hope this helps you get started. I'm very tech-phobic, but I learned the above over my first month or so. I'm still learning too.

Cheers