Macro options (basics)

[Shiva_42]

Could someone point me to a "technical" discussion/page, especially with drawings or diagrams, of how extension tubes/bellows work with "normal" lenses as opposed to actual macro lenses? I need to understand the differences of DOF, bokeh, etc... In particular I would like to see HOW the extension tubes or bellows actually accomplishes the "macro/micro" focusing look, 1:1 ratios, etc... Do extension tubes or bellows have any OTHER useful purpose other than the expected macro uses?

I know this is sort of a broad topic, that's why I'd like to see the technical side of it. THX!