What's the difference between stratified sampling, simple random sampling and systematic sampling? When will they be used separately?

There are two kinds of simple randomness, one is the lottery method and the other is the random number table method. Stratification means grouping people when there are obvious differences, and then each group adopts stratification or simple random sampling. The system is to divide the population into several balanced parts and extract them from each part according to certain regulations. If the population is not divisible by the sample, the remainder can be eliminated, but the probability remains the same.