Hello, Brooklyn,
Iron(II) means that iron has an oxidation state of two - It will give up two electrons in a reaction, Sulfur is in Group 16 on the periodic table. It has 6 valence electrons, but would like 8 to give it a full valence shell, (a lower energy state). Two more electrons would give it an electron configuration similar to argon, Ar.
Iron is willing to give up two electrons and sulfur wants two electrons, so we have a 1:1 correlation.
1Fe + 1 S = 1FeS (Iron(II) sulfide)
===
This question raises a trickier problem that I'll assume is beyond the scope of your question. But it is useful to take a look at other forms of iron sulfides, since it forms alternative structures that just FeS.
Iron pyrite, also known as fool's gold, has a formula of Fe(II)S2. It occurs because of some additional bonding between the two sulfurs.
It would be difficult for me to predict this would be a possible outcome of this reaction, but it is a useful perspective on how things may not always align with the first principles of reaction chemistry Products depend on temperature, pressure, and the presence of impurities.
=======
Bob
