I need some macro creation tips, please!

[Umo]

I know how to put the action on a hotbar, I want to know how to put it in a macro so I can also put other things in the macro which is what macros are for. Clearly no one knows, maybe someday they'll put out a list of what works.

There's no command for summoning mounts, so you can't put it in a macro.
On a side note, there's already an official list of commands you can peruse at will: Text Commands > Battle Commands

PS. If you're that concerned, you can make a separate macro with the rest of commands you may want to use and place it right next to the mount skill, although I can't even imagine what do you really want to do since all you can do when mounted is performing emotes. Maybe you're referring to companion instead of mounts? If that's the case, there's no command to summon your companion to battle neither.