[Seerah]

The vararg (...) merely represents a variable number of arguments. The game client passes through two arguments to each Lua file in an addon. Think of it like the Lua file is contained in a function that executes it, and it looks like this:

function ExecuteFile(...)
     --all Lua file contents, functions, etc, etc
end
 
ExecuteFile()

That means that if you assign the vararg to variables in your file in the main scope (outside of any functions or other blocks of code, usually done at the top of your file) then you can have access to what Blizzard is passing through to your file.

The two arguments are 1. the name of your addon, and 2. a table that is local to all files in your addon's folder. Think of this table as being a hybrid of a global and a local. It's global in that you can access it across all your files, but it's local in that nothing outside of your addon knows about it. So now, imagine that the game is doing this:

local addonName, addonTable = "Name of Addon", {}
 
function ExecuteFile1(addonName, addonTable)
     --your file contents
end
 
function ExecuteFile2(addonName, addonTable)
     --this file's contents
end
 
ExecuteFile1()
ExecuteFile2()

So, at the top of each of your Lua files, put this line (note, you can use whatever variable names you want, and they can even be called different things in each file - they'll still reference the same things):

local addonName, addonTable = ...

Now, anything stored in the addonTable table can be accessed in each file, and the table may be added to, etc. from each file.