Cross-posted to sci.electronics.basics which is a more appropriate place for this level of question. Followups to sci.electronics.basics
These are indeed very fundamental pieces, and defined in IEEE 802.3 (definition freely available on the net via a quick google search). They don't interface directly externally to a PC - MII is 'Media Independent Interface', so called because the physical layer is not a data pair, but logic signals.
PHYs and MACs interface to a processor (of some description) on the command port (MDC/MDIO usually, but there are others, especially SPI) and to the ethernet transport layer either through magnetics (for cables) or capacitive coupling for ethernet over backplane (been there, done that). MACs and PHYs connect to each other through MII/RMII/GPSI.
I'm not going to fully define their operation for you - get a datasheet and read it. A typical datasheet is at:
(AM79c901A home networking PHY)
One clue is this - MAC (Media Access Controllers) and PHYs (Physical layer interfaces) are usually separate for ethernet. The way they communicate is what you are looking at above. MII is very common, but so is GPSI (General Purpose Serial Interface).
That's the data port. There's also (usually), as I mentioned, a command port running either MDC/MDIO or SPI.
MACs and PHYs each provide different functions.
Once you have looked through the datasheets and app notes, (which will give you an idea of the operation of the devices), come back and ask again. It's not unwillingness to answer the question, but we do appreciate questioners who do at least some legwork.
How do i make them
Connect them up appropriately :)
Seriously, it would take a long time (and pictures) to explain their operation - I suggest reading available data sheets and application notes to get the basic idea. Try AMD and Intel for starters.
Apart from that, if you don't apparently even know what DTE means, it would be difficult to explain it