From experience, breaking stuff is one of the best way to learn - if you’re willing to take the time necessary to analyze (or guess) and attempt to fix it 
Trial and error is literally how I learned programming. I was too frustrated of willing to code (or at least modify existing programs) and only seeing those gibberish line of codes, so one day when I was young I decided “fuck it let’s change this number and see what it does” and 15 days later I’m maintaining YunoHost (and still have no idea what I’m doing anyway, ha !). One of the very first thing I did back in the day was to translate a game from English to French just by naively editing the .exe file with notepad xD.
Anyway, unfortunately there’s not yet any video tutorial on YunoHost packaging (though it’s been discussed here ?)
There are however various pages of documentation in here YunoHost • index and you may start here : YunoHost • index
One example of very simple application is anarchism_ynh (at least the old version) : GitHub - opi/anarchism_ynh: Yunohost implementation of the debian anarchism package
- you might want to read the
manifest.json - and the install script in the
scripts/folder
It basically just installs the anarchism package, which corresponds to some sort of manual about anarchism theory or whatever - and makes it available to an URL. So it’s a very basic static app
Then it all depends how familiar you are with command line and being able to install yourself an app “by hand”. We like to say that if you are able to install an app “by hand” (e.g. by following the official tutorial from, let’s say, wordpress) then you are pretty close to being able to package it as it’s ~pretty much putting all the steps in a bash script.
The best way to learn is to take an app that’s not already packaged (e.g look at the wishlist, see if there’s anything you’d like to have), try to install it by hand, and then create a first application for it. For example conversejs could be something nice to have
Anyway, feel free to come chat with us and ask questions on the dev and apps chatrooms : YunoHost • index