Begin badly, begin with questions (write them down), begin with a line that pops into your head or a few words you force from your pen. Begin with a character whose only partly visible to you, with eavesdropping in a cafe or on your own memories or imagination.
Begin though the critic rises up in your head with its brutal commentary. Begin to learn to ignore the critic, who knows nothing about writing and less about beginning.
Let your characters begin. They, too, will begin simply, tentatively, full of uncertainty, self-criticism, and the desire for what is easy and comfortable. They, too, will face voices that urge them to stop. But as your and their investment in their action rises, you and they will move past the simplest solution and onto better ones. Your collective determination will rise, in the face of obstacles and detours.
The journey will take you far and wide. Still, before you can move further, deeper, you must begin.
A Practical Alphabet for Writers: Find all the letters so far at https://bookwritingworld.com/blogs/