Question

The difference between the point estimate such as the sample mean and the value of the population

Answer 1

A sample is a subset of a population smaller in size. We study sample statistics in order to infer population statistics from them, since it is difficult to study population statistics directly, owing to its large size.
Now, when we talk of point estimates like mean for a sample, we refer to the value of that point estimate for the sample of data chosen out of the population, and when we refer to the value of the point estimate for the entire population, we mean the value of the point estimate for the entire population, not just the particular sample.
The value of a specific point estimate, like mean, may be different for the entire population and the selected sample, and may also vary from sample to sample.