How does Elon Musk's Neuralink brain chip actually work?

For the past six years, Elon Musk has been working on a chip designed to be implanted into human brains, with his neurotechnology company Neuralink. His ultimate goal is to develop a'brain-computer interface' that will initially be used to help people with paralysis or motor neurone disease to communicate. It will allegedly allow them to operate computers and mobile devices using their thoughts, but could have further uses in years to come. So what exactly is the chip? How does it work and how will it cure all medical problems?