Around minute 1:45 you open a new panel to load your reference image into, but there was no explanation of how to do it.
I don't know how Ken did it but for other people coming here, this is an equivalent way to do it: you go to the very bottom of the Properties where you want your new panel, right click the border at the exact place where the cursor changes shape, and select "Horizontal Split", then you drag your cursor to indicate where the new panel should appear.
Yes, that is a way to do it.
Alternatively, you can hover your mouse over any of the four corners, until your cursor changes into 'a plus sign without the center'.
Then hold the left mouse button and drag up/down (for a horizontal split) or left/right (for a vertical split).
Might be a bit finicky at start (can't remember if it was...), but super fast when you get used to it.
danielwilches Also worthy note to mention is collapsing the areas. Do as spike suggested when the mouse curse turns into a Cross-Hair/Plus sign you can alternatively click with the non-active mouse button (right click if you are a left clicker for everything or vice versa) and you get a context menu with a lot of options such as:
Vertical Split
Horizontal Split
(Join Areas) this one won't appear unless you already have a split area that you want to turn back into 1 area again. Super useful if you want to simplify back again
(Swap Areas) this also won't appear unless you have already split into 2 or more areas. It swaps between the two divided split sections between closest to your mouse.
You stick to the heavy lifting. I'm more of a dumbbell kinda guy. I can help on the smaller stuff haha.
