What does random sampling mean? How to randomly sample?

Random sampling means that the survey units are completely randomly selected from the population without any grouping, classification, queuing, etc. The characteristics are: the probability of each sample unit being extracted is equal, each unit of the sample is completely independent, and there is no certain correlation and exclusion between them. Simple random sampling is the basis of other sampling forms. Usually, this method is only used when the overall unit difference is small and the number is small.