It’s a very tedious task, especially so if the board shape is not square. Essentially you have to do everything by hand. The new openGL mode makes this quite a lot easier, as you can drag lines and arcs as needed.
My most “professional” panel is this one:
It’s got a frame, fiducials and tooling holes. I made the panel as an exercise and would only do it gain, if I absolutely had to (P & P assembly + paste stencil etc). For hand-assembled boards I would let the PCB manufacturer take care of everything and get individual boards. Some of them for some reason even charge you a “self-panelization” fee.
Unfortunately kicad doesn’t support cloning of boards. You will have to redo the whole panel if the design has changed, which is painful if there are a lot of small boards on the panel.
TLDR: simple panels are quite easy, anything else gets tedious very quickly.