The development of a human fetus changes by weeks or even by days. It is not possible to provide a detailed description of the appearance of a human fetus, because it changes as the different parts of the organism develop.
At 4 weeks, it begins to develop the structures that will form its face and neck, but it does not look like a baby yet. At 8 weeks, it is more or less half an inch in size and, by week 12, it measures about 2 inches and the sex organs start to become clear.
For more details, see also: The stages of pregnancy.