Adding a link, video or upload a file you hit the plus inside a circle just outside of the line you are on.
Writing is pretty basic, adding a link is best done if you hit space after the link is pasted in so that it will turn into a clickable link.
There really isn't anything magical on making a post here on the forums.
That is about it, no magic and no fancy ordeal.
Shalom, much love and respect one and all.