Joplin is a note taking application. This basically means that you create and write notes inside it. It is not intended to open external files (although it can import some formats which you can then edit inside it later on as notes).
In other words, if you're looking for a text/code editor which you can use to open and edit normal files, then Joplin is not it.
No need to set anything up . You can just install Joplin and use it locally. Now, if you want to synchronise your notes between multiple devices, then that does require additional configuration, but out of the box, Joplin is local first, so you don't need to connect it to any external services.
Have you tried actually using Joplin ? The notes are stored inside its database. In other words, there are no external files to edit, and you cannot use Joplin to open any external files either. Of course, you can create a new note and copy and paste text content from external files inside it.
By "locally" I mean that Joplin operates fully offline and stores everything on the disk. This doesn't mean though that you can access the notes as files, etc. using other software. You still need to open Joplin and use it to manage the notes, which are then stored in the Joplin's database.
I'm not sure if I can explain this in more simple terms .
No, Joplin has nothing to do with neither Git nor GitHub (except that the source code is stored there), so no such synchronisation is possible.
Yeah, I know. It sounds like I'm being dense, but during nearly 40 years of programming, I've never come across an editor that used a database backend in quite this way. Or, if I did, my brain refused to focus on it. You can ask any company/person I've ever worked with since the mid-90's and they'll tell you just how disconnected I am from database-think. My wife is an expert, so instead of trying to figure it out, I just get her to write any code that needs to deal with databases. It's actually a bit embarrassing. (well, not really! ) Give me any other kind of coding task and I'm there with bells on!
Anyway, thanks for clearing that up. Since MarkdownPad is no longer being supported (despite being a pay-for-the-pro-version app) and it's getting frayed around the edges with age, I'm on the hunt for something that will allow editing of .MP files directly. I love the way Joplin works other than the whole no-local-markup-files thing, so I'm keeping it in my toolbox until I find an editor that works more or less the same way. Until then, I can live with copy-n-paste. At least I know how that works!
Joplin uses the database approach, but there are other note taking applications, which operate on text files directly. Obsidian seems to be very popular and is often mentioned on this forum as well. However, please keep in mind that in contrary to Joplin, Obsidian is not free and open source software.
On other hand, if you want to store your notes in Markdown (or any other text format) and organise them in folders as you wish, you could also just use any code editor to open and modify them.
Joplin also supports File System Sync, which is good for sneaker net type of scenarios and moving between computers when a sync service isn't available. I used File System Sync and syncthing between three devices before I realized I had webdav access, then migrated to that.
You could put the file System Sync output out to git. Although I am not confident it is editable and then importable back into Joplin. Edit: as noted, these files are not intended to be edited.