We know that earth is tilted at a particular angle and also revolves around the sun. Different parts on the earth get more or less amount of the sunrays which cause the seasons and length of days and nights.
This can be easily understood by performing an experiment. Take an apple and pass a stick through it and shine a light on it. This will be summer, the light spreads more of the earthâ€™s Midwest and it will experience a longer day. Now revolve the earth around the sun where the other side faces towards the sun and now the ball is tilted away from the sun that will be winter. The light there will not spread out large so we experience shorter days in winter.
Others believe that days are short from June to December in the northern hemisphere of the earth and in southern hemisphere days are short from December to June. So they are not short only in winter or in the Midwest.
During winter sun rises from the south of east not exactly in the east and sets in the south of west not exactly in the west. After the winter solstice which is on 21st December the path of sun gets a bit high in the southern sky. And also rises and sets closer to the east and west respectively. The day where it rises exactly in the east and sets exactly in the west is known as the spring equinox on March 21st.