Just watch the next two.
At which point you can then dive into maybe the single most written about film series in the last 50 years.
There's:
Skywalking by Dale Pollock
Mythmaker: The Life and Work of George Lucas by John Baxter
if you wanna learn just about Lucas.
The Making of Star Wars
The Making of The Empire Strikes Back
The Making of Return of the Jedi
all by J.W. Rinzler
Which are some of the most comprehensive looks at what happened behind the scenes. For more old-school looks, there's also
Once Upon a Galaxy: A Journal of the Making of The Empire Strikes Back by Alan Arnold, which was used a lot in Rinzler's book, but is a good read on its own.
Do NOT read "The Secret History of Star Wars." People will link it, but they either don't know or don't really care that the entire endeavor is largely drawn from the same resources as the ones I've listed above, and mixed with a fair amount of conjecture and slant intended to drive home the theory that Lucas was an uncreative dipshit who stumbled into success when he married Marcia Lucas, his wife, who was the real reason anything worked, explaining why as soon as she left, his creative output suffered.
It's basically "Confirmation Bias, the book," despite the fact there are some interesting factoids in it.
