Taking a sample and giving a survey is one of the most common ways to get information about a large population. Doing every step well is important though, otherwise your claims may be not accurate. This tutorial covers some of the basics of samples and surveys.
An experiment assigns some subjects to receive a treatment while others don't get the treatment. Experiments also try to control for other variables so we can see if there's a cause-effect relationship between the treatment and some response. Learn more about the differences between observational studies and experiments in this tutorial.