A question about objects

I've been studying ASP for a week now, reading tutorials on the 'net, etc. But there's one thing bothering me. In the following example:

Set objFSO = Server.CreateObject("Scripting.FileSystemObject")
Set objDat = objFSO.OpenTextFile(Server.MapPath("file.txt"), 1)

I understand that objFSO is an instance of the FileSystemObject. I also understand that OpenTextFile is a method of that object. Why am I creating another object then, objDat? Does OpenTextFile return an object? Are there any subobjects?

p.s. by creating objDat you are creating an instance of a class/method/property inside the file system object. As you can see it is easier to type the one on the bottom rather than the one on the top...