Welcome @demon! There are a lot of important parts of posting, but I'll give you the basic ones:
To post an image - 
To italicize - text
To bold - text
For headers- #text or ##text (## is bigger)

I just wrote about my favorite tools on Steemit that really helped me when I was getting started, really helpful for beginners: I recently wrote about my favorite Steem tools, they are particularly helpful for new Steemians: https://steemit.com/steemit/@baodog/3-best-steemit-tools-for-beginners-earn-steem-gain-followers-and-track-progress