I didn't ask which of the recommended apps you installed/downloaded.
Bear in mind that "asciidocfx" is a java application which has its own specific idiosyncracies. It might start from the "launcher" but I'm not sure ....... personally I'd never recommend a java app to a novice user so I'll leave that to @Thanatermesis (who recommended it) to explain.
If the package is a ".deb" package it might pull in the required dependencies correctly but again, I'm not sure. 
I do know that "typora" (and "zettlr", albeit a tad less stable) offers the same functionality (and more, sans java) as do others (https://alternativeto.net/software/asciidocfx/) in which "zettlr" (which is FOSS) is conspicuously missing IMO. The "typora" page explains how to add their repository to your machine (Install Typora on Linux - Typora Support) and after that it will upgrade along with the other software and show up along with your other office applications in the launch-menu. IMO its a very well made program.... one of those I'm gladly financially supportive of.
- If you're in "free-mode" it will pop-up a nag-screen every now and then but we're used to that on Elive.
OTOH I would advise at looking at and playing with "ghostwriter" first, which should already be installed on your machine. It probably wont be fully what you're looking for but will give an idea of what's possible with markdown (it's a bit clunky, admittedly). Most other, more sophisticated apps will follow about the same work mode.
We have had a discussion on which of the markdown editor apps to include on Elive and "ghostwriter" came out on top. Markdown editor included by default for various reasons.
- Maybe "zettlr" is a better default candidate now.
Then again ... all conversions/exports (on linux) rely on "pandoc" which reminds me of:
