IIRC Hindus invented this number system (with glyphs for 0-9), and then the Arabs starting using it. Eventually the west started using them and credited the Arabs.
As for how they are written, everyone used the same shapes, and then they probably just ended up changing over time (“Hmm…how do I write that number again? Oh whatever I’ll just make it up”)
Feel free to do your own research though.
Zero was (in its modern form) invented in India. It’s pretty fundamental to the concept of Hindu-Arabic numerals too: it’s how we represent numbers such as 10, 100, and so on.