Just start pressing keys. Doesn’t matter if what you’re writing makes sense or is meaningful. Try not to use a lot of pauses in the writing. By that I mean commas and double hyphens. Pauses in thought. Interruptions between words getting on the screen. Out of your head and in front of you. Writing is half the physical act. Waiting for the thought to form is a related but still separate part. And with a lot of focus, a little patience and luck you can get to something worth reading.