There are so many ways that you can get started as a writer, one of the most common is by dipping your toes into some genres of books. Every single writer has their influences and that one book that acted as the gateway into their book obsession and is the reason that they now have to dedicate whole rooms in their house to books that will die before reading. Now, if you want to get started as a writer, I've got a few quick tips to get you started.
Writing prompts
Writing prompts - like the ones I write for example - are the best way to kick-start your engines for writing. This is because you don't have to spend resources turning the blank page into something and instead having a hand to he'll you turn it into a less blank page. The great thing is it's already there for you. However I want to stress that it's still hard and you aren't going to beginning writing and then write a best selling novel the next day, it takes time.
Another method for you
I can recommend picking the first line and the last line of any book and trying to connect them. If you're stuck, I'd advise you to go and get a random book, use it as the next line. I might do a short story based on this and put it here!
Overcoming overthinking
Overcoming overthinking and creative self doubt is very difficult and I can't say that it's an easy move. However my best tips are to try and believe in your own writing voice and that you have a story to tell in your own way. Writing is an art form and because of that you can express yourself in whatever way or medium you feel is right - a novel, play, script of some kind, ect - and that's amazing.