And Apple paid to see what they were working on in the lab. As I recall Xerox even got Apple stock out of the deal. So again, DIDN'T STEAL.
Apple did not pay Xerox.
During 1978-80, Apple was looking for venture capital, and so was offering angel investors pre-IPO stock options. One of the several takers was Xerox Development Corporation (XDC), a financial investment branch of Xerox.
Jobs used the XDC investment connection to talk his way into a demo by PARC, an entirely different division. However, Apple themselves have never claimed that this included a license, not even when Xerox sued them years later for failing to cite Xerox as a base source for their GUI.
What Xerox showed them was also CRUDE. Apple took this idea and expanded on it big time. Among other things, they developed overlapping windows, which they *THOUGHT* they saw at Xerox. They didn't. Xerox was surprised when they showed it. It took Microsoft quite a while to figure it out and do that in Windows.
Not your fault, but that's a commonly repeated myth started by people who (as so often happens) didn't understand what they were reading, and so made up something incorrect that they could understand.
Xerox already had overlapping windows. They also had a fast blitter algorithm, so they simply redrew everything underneath when the topmost window was moved.
What one of the Apple developers THOUGHT he saw at Xerox, was overlapping windows that only updated the screen regions that had just been uncovered. So he wrote his code that way. Nice, but this is something that any GUI developer does if they have the time (or the need because of a slow system). Did it myself in the early days. It's not rocket science.
Interestingly, Xerox found through testing that most office workers immediately arranged their windows to be non-overlapping (as many people still do on large or multiple monitors), so one version of their GUI defaulted to tiling windows on startup. I suspect this fed the myth as well.
In addition the PARC developers tried to hold back showing the best stuff, since they were convinced that Apple was going to steal it all.
All that said, Apple did add many of their own innovations, of course, as did others.