Elemental sulfur as a proton number of 16, and hence an atom of sulfur has 16 electrons.
Using the spdf orbital model -> 1s2 2s2 2p6 3s2 3p4. There are three 3p-orbitals (3px, 3py 3pz), and each orbital can hold 2 electrons.
There are only 4 electrons allocated to the 3p orbitals, thus there is space for 2 more.
Also having a principle quantum shell number of 3, it means that there are 3d orbitals as well that are available, if necessary for “expansion of octet” / hybridization to form 5 covalent bonds e.g. in H2SO4