[development] Metadata question

[Gabriel Rossetti]

Hello,

I am trying to figure out how metadata is used in Drupal and I'm a bit lost.
I am going to add new metadata to objects (nodes?) for a project I'm 
working on,
and I came across flexinodes, node, taxonomy, relationships, and I need 
someone
to clarify things up some for me. Are all things stored as the same 
object? Is an attachment
(pdf, doc, jpeg, etc) stored as the same thing? Does it have metadata? 
Does regular content
(non-attachment) also have metadata? Is it also stored like attachment 
metadata (if it has some)?

Thank you,
Gabriel