Crappy first drafts. Anne Lamott phrases it slightly more colorfully, but that's the gist. Can't write? Don't wait for the Almighty to hand you a perfectly formed manuscript from the sky. Put pen to paper or fingers to keyboard and just write. Will what you write fall somewhere beneath the quality of a poop emoji? Often yes. But you're trying and that is a heck of a lot better than not.
And maybe, just maybe in that crappy first draft is the seed for a slightly better second draft. Maybe that buds into a not terrible third draft and--if you cultivate, water, and care for the words--maybe it blooms into something beautiful. Maybe. But you have to start writing before any of that is remotely possible.