You don't stand the remotest chance of understanding it. You can therefore say "What?" and "Eh?" and even go cross-eyed and start to blither if you like without any fear of making a fool of yourself.
The first thing to realize about parallel universes is that they are not parallel.
It is also important to realize that they are not, strictly speaking, universes either, but it is easiest if you don't try to realize that until a little later, after you've realized that everything you've realized up to that moment is not true.
The reason they are not universes is that any given universe is not actually a thing as such, but is just a way of looking at what is technically known as the WSOGMM, or Whole Sort of General Mish Mash. The Whole Sort of General Mish Mash doesn't actually exist either, but is just the sum total of all the different ways there would be of looking at it if it did.
The reason they are not parallel is the same reason that the sea is not parallel. It doesn't mean anything. You can slice the Whole Sort of General Mish Mash any way you like and you will generally come up with something that someone will call home.
Please feel free to blither now.
Ford Prefect's original name is only pronounceable in an obscure Betelgeusian dialect, now virtually extinct since the Great Collapsing Hrung Disaster of Gal./Sid./Year 03758 which wiped out all the old Praxibetel communities on Betelgeuse Seven. Ford's father was the only man on the entire planet to survive the Great Collapsing Hrung Disaster, by an extraordinary coincidence that he was never able satisfactorily to explain. They whole episode is shrouded in deep mystery: in fact no one ever knew what a Hrung was nor why it had chosen to collapse on Betelgeuse Seven particularly. Ford's father, magnanimously waving aside the clouds of suspicion that had inevitably settled around him, came to live on Betelgeuse Five, where he both fathered and uncled Ford; in memory of his now dead race he christened him in the ancient Praxibetel tongue.
Because Ford never learned to say his original name, his father eventually died of shame, which is still a terminal disease in some parts of the Galaxy. The other kids at school nicknamed him Ix, which in the language of Betelgeuse Five translates as "boy who is not able satisfactorily to explain what a Hrung is, nor why it should choose to collapse on Betelgeuse Seven."
PRESIDENT OF THE IMPERIAL GALACTIC GOVERNMENT
The term Imperial is kept though it is now an anachronism. The hereditary Emperor is nearly dead and has been for many centuries. In the last moments of his dying coma he was locked in a stasis field which keeps him in a state of perpetual unchangingness. All his heirs are now long dead, and this means that without any drastic political upheaval, power has simply and efectively moved a rung or two down the ladder, and is now seen to be vested in a body that used to act simply as advisers to the Emperor- an elected governmental assembly headed by a President elected by that assembly. In fact it vests in no such place.
The President in particular is very much a figurehead- he wields no real power whatsoever. He is apparently chosen by the government, but the qualities he is required to display are not those of leadership but those of finely judged outrage. For this reason the President is always a controversial choice, always an infuriating but fascinating character. His job is not to wield power but to draw attention away from it. On those criteria Zaphod Beeblebrox is one of the most successful Presidents the Galaxy has ever had- he has already spent two of his ten presidential years in prison for fraud. Very very few people realize that the President and the Government have virtually no power at all, and of these few people only six know whence ultimate political power is wielded. Most of the others secretly believe that the ultimate decision-making process is handled by a computer. They couldn't be more wrong.