Answer:
So basically the rows are called periods, and the columns are called groups. The groups show that those elements have similar characteristics. There are also different families such as the noble gases and alkali earth metals. The elements are placed where they are because of the atomic number which is directly equal to the number of protons there are. The atomic mass is the number of both protons and neutrons. Also, even though the number of protons can be equal to the number of electrons, that isn't always the case. It could be an isotope which is basically for when an element or atom isn't neutral. Umm, so, I hope this helped. I know it's very long but if you need anything else just ask!! c: