{ 1 } - an illusion is a perceptual situation that tends to fool us, while a delusion is something that is seriously wrong with us.
{ 2 } - illusions and delusions are the same.
{ 3 } - an illusion is where you refer to someone else's writing, while a delusion is where you lie about something.

Illusion examples: where one of two equal lines seems to be longer, where the magician seems to saw the woman in half, and where the wheels of the truck seem to spin backwards.

Delusion examples: delusions of persecution, delusions of grandeur, and other cases of grossly disordered beliefs.