Klaatu can't fly the ship.
Gort* flies the ship.
Klaatu 'tells it where to go' like the computer reference in comments.
You don't need to know how to manufacture a computer to know how to operate one.
"How does a computer work?"
"Some kind of electricity, makes bits
move around... ermmm... with chips & ermm... wifi..."
*Gort may not actually pilot the ship physically, but he appears to be connected to the 'computer' that does. In 1951 the concept of 'computer' was rather hazy compared to today.
After comments - clarification of "how does xyz work?"
& probably more salient to the era in which the movie was made than any kind of expected "accuracy" in Klaatu's explanation...
In the 50s, society was still reeling from WWII, nuclear power was still in the 'It goes Boom!' phase but the man in the street was being told that it was the future of mankind, the saviour of 'energy' [which really hadn't had anything of a 'crisis' yet]
So, for 50s Sci-Fi, everything vaguely futuristic had to be "Atomic-Powered"
For the as yet naïve population, it was an answer in itself.