Sampling techniques

W​‌‍‍‍‌‍‍‌‍‌‌‍‍‍‌‍‌‌‌‍​hat are the different sampling techniques and how to select the most appropriate one for the re​‌‍‍‍‌‍‍‌‍‌‌‍‍‍‌‍‌‌‌‍​search? + example?