To begin as simply as possible, start punching any and all words/sentences you can think of into your word processor (or pen to paper if you prefer), don’t worry about how insane what you type sounds, just type. Think of it as a dream you are having where anything can happen; you may be walking along a road that stretches for miles, then there is someone next to you and they’re talking about how they love to travel, suddenly you are in Egypt, etc.
That’s very basic, don’t stop there, write anything that pops into your head. It could be that your arm becomes disconnected from your body and moves by its own accord, it finds a snake and they have a ‘romantic’ time together. An enormous tidal wave washes that away and you see from the corpses floating around you that the entire planet has been engulfed by floods killing all land life.
Sentences don’t need to make sense, words don’t need to be spelled correctly and a full stop doesn’t need to be used at all. Just go!
Everything I have just mentioned sounds absurd, but this is how I first began to write. I later learnt that there were books written on this style/exercise of writing. It’s called free writing or also stream-of-consciousness writing. Look it up if you like.
This should free up your mind and prove that you can write. After writing for fun with no direction, you can begin moulding a story that you are interested in and making it your first short story or novel.