The book "Personality" by Nettle gives the best layman's summary of the Big 5 model I've found. What I particularly like about it, beyond the summary of each as

The book "Personality" by Nettle gives the best layman's summary of the Big 5 model I've found. What I particularly like about it, beyond the summary of each aspect, is the way he frames it in terms of evolution and why being on one end of the scale for a trait is not "better." Agreeableness is probably the easiest one to understand from an evolutionary perspective. If you worry a lot about other people's needs, you're more likely to make them happy and reap the benefits of reciprocity, but you're also less likely to directly pursue your own needs. So it goes with the other traits too: being on different parts of the spectrum come with advantages and disadvantages from a reproductive standpoint. Conscientiousness and Neuroticism are the two traits most correlated with financial success in the modern world, but they had downsides in an ancestral environment and even in our modern world can have negative effects e.g. on personal happiness and wellbeing.