The Population Report gives you summary information about the entire population of candidate solutions maintained by the Evolutionary Solving method at the end of the solution process. The Population Report can give you insight into the performance of the Evolutionary method as well as the characteristics of your model, and help you decide whether additional runs of the Evolutionary method are likely to yield even better solutions.
For each variable and constraint, the Population Report shows the best value found by the Evolutionary method, and the mean (average) value, standard deviation, maximum value, and minimum value of that variable or constraint across the entire population of candidate solutions at the end of the solution process. These values will give you an idea of the diversity of solutions represented by the population.
How you interpret the Population Report depends in part on your knowledge of the problem, and past experience solving it with the Evolutionary method or with other Solving methods. For example, if the Best Values are similar from run to run, and if the Standard Deviations are small, this may be reason for confidence that your solution is close to the global optimum. However, if the Best Values vary from run to run, small Standard Deviations might indicate a lack of diversity in the population, suggesting that you should increase the Mutation Rate and run Solver again.