When I started writing fiction I was lost. Where/how to start? So many ideas! Snippets of dialogue spinning around in my head. Finally I decided I would just start and see what happened. And things happened...oh boy did they happen! But 100 pages in I still had no idea where it was all "going."
I was being lead by my imagination. Okay, better that than not writing. But it does get frustrating. Then a workshop leader asked me how the story would end. "End?" I still didn't really know where it should start!
"Aim for the target," they said. Aha! That cleared it all up for me. It didn't make writing a breeze but it kept me focused. I fretted over the ending for a long time. But it was worth all that fretting because once I knew the end, I knew the beginning! Now I had to "connect the dots."
In fact, eventually I learned to work backwards. (Sometimes forward and back at the same time.) Outlining became possible. "Plot" stopped being a 4-letter word.
So, if you are stuck with "where to begin?," change the question to "where to end?" I bet that helps!