'What if...? questions are the initial idea. They are the premise from which a chain of events can occur. My WEA student, Philip, described them as 'the flint which sends sparks to light the fire.'
Think of Romeo and Juliet. The 'What if...?' might have been:
What if two teenagers from rival families fall in love?
From there spins out the rest of the story: fights, drama, marriage, death, and suicide.
Read this excellent story by Ray Bradbury, 'There will come Soft Rains', and try to work out what 'What if...?' question, Bradbury might have started with.

(If you liked this story, you can click here for a dramatisation of Bradbury's 'The Martian Chronicles.')
So now it's your turn. Think of something that interests you. It needn't be as dramatic as a nuclear explosion. It could be that your hobby is knitting. Your 'What if...?' questions might include:
'What if everything I knitted held my hopes and fears?'
'What if I could knit other people's dreams?'
'What if the jumper I knitted killed someone?'
The list is endless and each one could spark a story idea. If you are stuck, you only have to turn to the news:
'What if Trump built that wall?'
What if my family and I had to flee a war-torn country?'
'What if Alexa ordered me a new husband?'
That was the easy bit. Now all you have to do is write the story...