If you can see and touch something, or hear something, you can be convinced that it exists in what you deem to be reality. White cars are unlikely to present any difficulty to most people, but many of the topics to be discussed later cannot be directly perceived by the five senses. This is very important to understand. With theories which are not directly observable, the theory only becomes acceptable when tested, agreed and reproduced by a number of learned colleagues. The creation of the Universe is not something any scientist on Earth has personally observed, but by understanding the physical universe, its behaviour, matter and particle physics, credible explanations can be advanced.
Memory is important.
And the logical, thinking mind is useful for piecing together evidence and advancing theories when there are gaps - courts of law run this way. Whilst nobody actually observed who broke the window and took the jewellery, by piecing together the facts using logic and the thinking mind, a credible theory may be advanced which may be correct. This is the starting point. And the point of the example of the white car is to get you thinking about how believe or verify that something is true. With simple everyday things it is easy.