You may have heard of automatic writing or "stream of consciousness". If you want to do it like the surrealist poets, write at speed, without stopping, without plotting or planning, without worrying if it's "good" or if it makes sense (in fact, the less sense - the more abstract and strange it is - the better). Just let your mind wander - let the words spill from your brain onto the page in whatever form they come.
"I don't know what to write so the cousins of the fourth temple made their appearance suddenly and the erstwhile pyramids scheming like the eponymous elephants licked and supped at the tertiary sector's best people who were stood with clipboards and fathoming the depths of their collective wisdom brought orange juice and sandwiches for all and sundry when the sun came up and the moons of other planets began to form on the horizon..." etc., etc.
Now your turn!
*Hint: if you don't know how to start, pick a line from the writing above, and use this as your beginning sentence; then whatever comes into your head after that is GOLD. Just keep writing!