Control: the sample in which nothing changes. It stays constant throughout the experiment.
Variables: This is the sample that will change. It is preferable to have less variables, because your results will be more accurate. By having more variables, it makes the process more difficult.
You need the control group, in order to have something to test against it, being the variable. Without it, your won't be able to conduct your experiment.
The actual process explained:
Come up with a question first. Do research about what you decide before trying to go through everything else involved.
With a Hypothesis, you think of what sort of experiment your are going to conduct, then you come up with a statement that you are going to try to prove/disprove. This is your prediction of what the outcome of the experiment will be.
Next you will need to test your hypothesis, by actually conducting the experiment. The process involved depends on what experiment you choose to do. As you go through your experiment, you will probably be expected to write down your observations and data you collect, as well as possibly keep a journal of these details. Be sure to list all supplies and equipment you use.
Next, analyze the results. Did your conclusions support your hypothesis? Did your statement prove to be correct? Be sure to state your conclusion.
I hope this helps!