Complex sentence: The girls wear either a green V-necked cardigan/jumper with a green striped tie (only if using a white sleeved shirt), a green skirt with black tights/socks or black trousers and school shoes.
Split into simpler sentences: The girls wear a green V-necked jumper with a green striped tie. A green skirt with black tights/socks or black trousers and school shoes.