If you want to manage passwords on KDE neon a good place to start is with KeePassX. It's a great program to create and store all your passwords in and it isn't hard to create a system to make your passwords available on all your devices.
To install KeePassX on KDE neon open up Konsole and type,
sudo apt install keepassx
After installation you can find it in the Applications Menu under Applications/Utilities or by selecting the Applications Menu and typing its name.
After opening the program the first time you will have to create a new database. After that it will ask you for the password for that database before opening it.
My system consists of a couple methods. I have a laptop, a desktop and an Android cellphone. All of which are using Firefox as the web browser. So I need a system where if I create a password in one I can use it in the others. To do this I use a mix of Firefox Sync and a file synchroniser. Currently the synchroniser is Mega as it offers 5GB of storage for free but any can be used.
It basically goes like this. KeePassX creates a password database that is locked by a single password (It's a good idea to choose a good one). I save that database into my file sync folder which means I can access it on any of my devices. On my devices using KDE neon I can use KeePassX to open it and on my Android phone I use a program called KeePassDroid. The only problem with this is that I can't create passwords in KeePassDroid but that is life.
Added to this I use Firefox Sync which synchronises all my passwords between devices so I rarely have to use KeePassDroid anyway as the passwords are already usually synced in Firefox. And that is it. Strong passwords everywhere.
(I do also occasionally also take a backup and place it somewhere in case the file sync hits a bug and corrupts the file as well. Backups, they are a good idea.)