Question: I'm looking for shortcuts that would help me to navigate directories quickly and efficiently.

Answer: 
If you [check the contents of the repository with a web browser](http://ppa.launchpad.net/videolan/stable-daily/ubuntu/dists/), you'll see that this repository does not have a directory for release named `bionic`.

This PPA seems to have ended support for release `bionic` or never had one. The repository name includes the part "stable-daily" which suggests it should have had frequent updates, but according to the "last modified" times indicated, this PPA has had no updates since 2017-07-21.

All the versions of Debian starting from release `stretch` (Debian 9, the current `oldstable`) now contain VLC 3.0 in the standard repositories, so adding a PPA is no longer necessary if VLC 3.0 is what you want. Since Ubuntu is based on Debian, the current Ubuntu versions will have at least that version too.

If you want [nightly builds of the latest versions of VLC](https://nightlies.videolan.org/), you might want to use the "master-daily" part of the repository instead of no-longer-updated "stable-daily". However, if you look at the [status page of the master-daily PPA](https://launchpad.net/~videolan/+archive/ubuntu/master-daily), it seems the latest VLC has just recently failed to build (1 hour 10 minutes ago as of this writing).

Now you'll have to first decide what you want to do, and update the repository configuration of your system accordingly. Look into `/etc/apt/sources.list` file and any files in `/etc/apt/sources.list.d/` directory to find the URL listed in the original error message.

If you simply wish to stop using this repository, you can comment out the line with this URL (or if it's in its own file in `sources.list.d` directory, just delete the file). 

Since the question tags say `debian`, the original repository is for Ubuntu, and you don't explicitly say which distribution you're using, I cannot recommend any particular replacement.
What that error messgae means is that apt thinks that the repository that you are trying to update from is a bunch of random code from the internet. If you do in fact trust this source however, you can turn off checking if repositorys are secure by using the --allow-unauthenticated flag after apt update (e.g sudo apt update --allow-unauthenticated). If that doesn't work, try the --allow-insecure flag instead.