The ailment under which Regulus suffered was extreme privilege. He'd never had to cook or bake or make a single meal in his life, he'd never made his own tea, never even made a simple cucumber sandwich. That, everywhere he'd traveled, was done by house-elves.
His privilege had left him ignorant of a great many things, the most pressing of which, right now, was the simple basic skill of making toast.
He looked at the loaf of bread and said, "Oh, I thought it was just... you know... baked that way." Which was not a wholly irrational thing to think when the only part of the process he'd ever seen was the end result: toast on his plate.
He leaned over and picked up the bag of bread and the jar of jam. "How do you... toast... toast?" he asked.
As for cleaning? Regulus also didn't know what Ned was talking about, and without clear instructions, he took no action in that regard.