Originally posted on 09/30/2017:
i take it you're an excel guy. the id, aka identifier or key, is a unique number used to relate tables to each other, a key concept of SQL or relational databases. maybe these pictures can explain it. SQL is easy to use and powerful, used by companies all over the world. you can retrieve bits and pieces from each table to combine new tables or views. it doesn't make sense to repeat data all over the place, you can structure your databases in a smart way to avoid duplicating data and write queries to combine the data when needed.
https://www.w3schools.com/sql/sql_join.asp
https://gfycat.com/SpicySevereIberianmidwifetoad