The various ways in which we can select samples can be divided into two types:
Probability Sampling: Some researchers refer to this as random sampling.
Non-Probability sampling: This is also referred to as non-random sampling.
Whether you decided to go for a probability or a non-probability approach depends on the following factors:
Goal and scope of the study
Data collection methods that are feasible
Duration of the study
Level of precision you wish to have from the results
Design of the sampling frame and viability to maintain the frame