Think of how you would answer these questions.
Scenario 1. A group of friends of yours have the opportunity to open a food trailer near your campus. They need to focus on one kind of food. What type of food should they choose? How could you obtain useful data to help them decide?
Scenario 2. You're working at a hospital that treats a lot of patients who are burned. They are thinking of doing an experiment to see whether Vit C, taken orally, and Vit E, taken orally, help burn patients heal faster. How would you expect that experiment to be set up?
Clearly there is not just one way to answer each of these questions. There are many correct ways. Some of the correct ways are better than others. There are also many incorrect ways. Despite the fact that this all sounds very confusing and not at all like anything you have done in math courses before, most students find these kinds of questions interesting, and have many correct ideas about how to proceed. That's because these are very real questions - you can envision what people in real life are interested in and you can think of what is perhaps ideal to do, but difficult to accomplish. Keep thinking like that as you study sampling in our course.
Here are some hints.
Scenario 1. In designing the method to take a sample, think about the population you're interested in. How will you choose to sample so that you have confidence that you sample is likely to be representative of that population? More to the point - what are the things you'll be tempted to do (to make it easy) that will mean your sample doesn't really represent the population? If you can't think of any of these now - then you'll have fun in our course where we think about some of the high-profile mistakes people have made in sampling over the years! You can empathize with them about how hard it is to really do this right!
Scenario 2: In designing an experiment, the basic idea is to set it up so that we can make some useful comparisons between the people getting the treatment and the people who aren't getting the treatment. Ideally we want those two groups to be completely alike except that one group gets the treatment and the other doesn't. It's not completely practical to do that always - so how do we do something practical that is as close as possible to our ideal?
When you learn about designing experiments in our class, you'll learn quite a bit of new terminology and structure. That can be somewhat overwhelming if you look at it as just a list of things to learn. It is much easier to understand if you have a basic idea for an experiment in mind (like this one about Vit C and Vit E for burn patients) and then try to think about whether / how you could use each of the ideas to design this experiment.
In sampling, the point is to get a representative sample from the population about which you want to discuss.
In designing an experiment, the point is to control the effects of all other variables besides those you are actually trying to vary in order to make comparisons. There are many ways to do that, in theory, and many of them are hard to carry out in practice. So you must understand the basic principles to design the best experiment that is practical to carry out.