To understand how evolution may work, we need to understand how long a few billion years is. Also we need to understand how diverse our biosphere is. Also we need to understand how random numbers work. No wonder, I encounter people, even among the biologists who have an easier time accepting fairytales than understanding how evolution can work.
I don’t have any suggestion to help you understand how long a billion years is. But I have a book to recommend, if you want to understand random numbers. It is one of the earlier books of Nassim Taleb called Fooled By Randomness.
In order to understand the biodiversity, just be more observant every time you go outside for a walk. After a few years of this, you will understand that even moving a few miles, changes the environment enough to cultivate differences in the kind of living beings that can thrive more effectively, and how varied that are.