How to send a file from my computer to my phone using KDE Connect?

Open KDE Connect on the panel, and from there you will see a small folder icon on the right hand side , click on it, it will open you files on your phone.

If you are running Dolphin file manager split the screen so that you have your android on one side and your computer files on the other side. Drag-drop, copy-paste and have fun.

I found that I had to restart my phone after copying the files over to my phone to actually show up on my android system, but copying from phone to computer was instant.