The main difference between a neurologist and a neurosurgeon is that one performs brain surgery while the other one doesn't.
A neurologist doesn't perform any brain surgery although they diagnose and treat conditions that involve the nervous system and brain.
A neurosurgeon is also a person who studies the nervous system and treats conditions with the brain and nervous system and also performs surgery on the brain and nervous system.
So they are similar to each other but the neurosurgeon as the name implies performs neurosurgery while the neurologist doesn't.
Also a neurologist also focuses on treating brain conditions and nervous systems conditions through medicines and other therapy and doesn't focus on surgery.
But they will refer you to a neurosurgeon for brain surgery or other nervous system surgery if it is required.