OK, here's the link you asked for:
https://steemit.com/steemit/@ace108/how-to-include-image-in-your-post-reference-to-using-steeming-com-in-include-pictures-your-post
For video, I didn't do before but I test once if you create a link to youtube video, it embeds automatically but for other video it does not. If you use the editor to put in a link, do enter the text first, e.g.., CLICK HERE, then highlight the text and click on the link icon in the Editor and you can then enter the URL for the link. good luck with that.