What should I write about? Why do I write? Am I a good writer? What am I doing trying to be a writer? What does it all mean?
Okay, on some level these questions have meaning. But then again, they don't. They're just pointless questions that delay and distract you from sitting down to write. And that just delays and distracts you from the practice you will need to become a better writer.
Less talk, more write. Stop asking unanswerable questions that interfere with your writing. And with all that extra writing time you'll free up by not asking so many existential questions, you might improve to the point where the "am I a good writer?" question becomes irrelevant.
What do you do when you're cornered and dispirited by these thoughts and questions? Use them. Channel them into writing. Write about your fear and emptiness, write about all your struggles with writing. Use these topics for practice. And improve.