"how punched cards were used" The first use was in tabulating the census of 1910, I think that was the year. They were invented by James(?) Hollerith. I am looking at a punched card right now. The card was divided into rows and columns.
There were 80 columns and I think 12 rows, the top 3 rows were called zones and indicated how the remaining rows were encoded.
Each column could be a letter(A - Z) or decimal number/(0 - 9). There are 26 letters so each zone punch along with one of the lower 9 was one of 9 letters -- 3 zones times one of 9 lower rows covered the 26 letters. I think this is accurate, no punch was zero and a punch in a lower row was 1 - 8. The cards were read by having a spring loaded contact that would fall through the hole so that whichever made contact that would be the meaning of the punched hole.