Fundamentals on database variable meanings

[jmcclure3699]

I have not been able to find in any of the on-line materials some very, very basic info on what the typical database headings mean and how the program works with those headings -- what the program has to know in order to function. I think I know what Source and Target mean, but I could use some basics on that; I'm not sure what Type means and how to assign that; it looks like "id" under "nodes" is giving every relationship a unique identifier?; when do I need to know (and what) about Modularity Class? I think I understand Weight but would like to know the basics of how to apply this. I primarily want to show strength of relationships within a matrix of interactions among economic sectors (an Input-Output table).