General Knowledge question about Databse structure and Logic

As you all know, I am completely new to this wonderful program. First, is there anyplace you know of where I can get a general overview of how to go about data modeling and the logic behind designing a database? I saw that one of the templates has a sub-table for example, which led me to think of why one would need a sub-table instead of just another table and having that be refered to from a table, my knowledge is that limited and i need to learn! My emails to Ninox about what I want to do have gone un-answered. I have a specific project I am working on and I have an Excel spreadsheet which mostly does what I want it to do, but doing it as a database would be, I think, more elegant and useful, considering I can change views on the go and see information in different relationships which is not as easy in Excel. Thanks in advance.