What do these differences tell us about the properties of a sampling distribution?

How is a sampling distribution different from the distribution of a sample? From the distribution of a population? What do these differences tell us about the properties of a sampling distribution?
What is probability sampling? Why are researchers encouraged to use this type of sampling if possible in doing their research?
If we took three different samples of college students (one from California, one from Arizona, and one from Alaska) and each sample had 500 students, what do you believe the sampling distribution for age would look like? What about for parent’s annual income? What about for number of snow days? Explain each response.