This type of argument usually takes an organ that appears (and is) complex such as the eye, And then this organ is pointed at by the creationists while they scratch their head and proclaim "man, that looks hard as shit to make". They then make the case that because they can't imagine how natural selection could have produce it that their particular god must have.
The truth is, No matter complex an organ is, Natural selection is perfectly equipped to produce it so long as this organ can be built in gradual steps with each step being beneficial. And the eye is an organ which can be produced like this (just like all organs in every organism).
The evolution of the eye is fairly simple once we understand how evolution works. It can even be seen in the development of a human fetus.