I find if you don't use the editor its much easier but you have to know the "hotkeys" to format your post.

#(space)Header - for big text

and then you can just insert url(web address) straight in for pics or you tube.

quotes

try this link for better understanding.

https://steemit.com/steemit/@lourenc/howto-styling-your-post-on-steemit-using-markdown