Use this scheme as follows. You first must know the orbitals. An s orbital only has 2 electrons. A p orbital has six electrons. A d orbital has 10 electrons. An f orbital has 14 electrons. You can tell what type of orbital it is by the number on the chart. The only exception to that is that "8" on the chart is "2" plus "6," that is, an s and a p orbital. The chart reads from left-to-right and then down to the next line, just as English writing. Any element with over 20 electrons in the electrically neutral unattached atom will have all the electrons in the first row on the chart. For instance, scandium, element #21, will have all the electrons in the first row and one from the second. The electron configuration of scandium is: 1s2 2s2 2p6 3s2 3p6 4s2 3d1 Notice that the 2s2 2p6 and 3s2 3p6 came from the eights on the chart (2+6). Notice that the other electron must be taken from the next spot on the chart and that the next spot is the first spot on the left in the next row. It is a 3d spot due to the "10" there and only one more electron is needed, hence 3d1.
The totals on the right indicate using whole rows. If an element has an atomic number over thirty-eight, take all the first two rows and whatever more from the third row. Iodine is number fifty-three. For its electron configuration you would use all the electrons in the first two rows and fifteen more electrons. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 from the first two rows and 4d10 5p5 from the third row. You can add up the totals for each shell at the bottom. Full shells would give you the totals on the bottom.
We have included an R shell (#8) even though there is no such thing yet proven to exist. The chart appears more symmetrical with that shell included. The two electrons from the R shell are in parentheses. We have not yet even made elements that have electrons in the p subshell of the Q shell.