KDE Connect is usually installed by default in KDE, (or in the repositories if it isn't) and then it's just a case of installing the app in Android and pairing them up. A persistent notification is usually required to keep it active and a few permissions to allow it to send notifications and send files etc.
Sending files from KDE to another device, such as your phone, is as simple as navigating through the Send To menu of Dolphin (KDE's file manager) and choosing the right device.
And on Android there's a KDE Connect item in its sharing menu. And you get notifications at both ends of file transfer progress and completion.
KDE Connect is not only useful for sharing files but also, amongst other things, for mirroring your phones notifications on your desktop, (and/or the other way), controlling multimedia shortcuts from Android, as a Remote input device (use your phone as a mouse and keyboard) and send custom commands to your desktop.
Android notifications pop up on the desktop just like the local toast notifications.
KDE Connect also shows the battery status of connected Android devices
Sending files from Android to KDE drops them in your Home folder.
Although Clementine music player actually has it's own app for controlling from Android, I usually prefer to use KDE Connect instead.
Remote Input allows you to control your KDE desktop using your phone as a trackpad and keyboard.
Run Command allows you to run various common commands to your desktop and you can add custom commands too. Plenty of useful preset commands (like shutdown, reboot etc) and also some interesting custom commands too, lots of possibilities - there's a full list of commands here. From that list, I've added a command to take a desktop screenshot and send it to my phone.
I am surprised that KDE Connect (and the Gnome equivalent) isn't written about more often, as it's such a useful tool, I find it particularly for showing notifications from my phone and controlling the media keys. I often find it much more convenient to use it to send photos from my phone to my desktop rather than plugging it in and dragging and dropping them. There are also early builds for Windows and Mac OS, amongst others, if you have those on your local network, and you can find them and more builds on the KDE Connect site. I have been using it on KDE for a long while now, when I moved back to KDE from XFCE, and it just keeps getting better with every release.