As per the Bohr' model of atom, electrons goes around the nucleus in circular orbits. These circular orbits are also called shells. The shell closest to the nucleus is called first orbit / K shell, It can hold maximum of 2 electrons. The shell next to K shell is L shell / second orbit and it can have maximum of 8 electrons. The third orbit / M shell can have 18 electrons.
While drawing the Bohr model of any atom we start placing electrons from the First shell to second and so on.
Sulfur atom has in it 16 electrons. Its K shell has two (2) electrons, M shell / second orbit has eight (8) electrons and the remaining six electrons are in the M shell / Third orbit. This gives Sulfur electronic configuration K (2) , L (8) , M (6).