The definition of science:

Science is not merely a collection of facts, concepts, and useful ideas about nature, or even the
Systematic Investigation of nature, although both are common definitions of science. Science is a method of investigating nature—a way of knowing about nature—that discovers reliable knowledge about nature. So science is a method of discovering reliable knowledge about science.
Reliable knowledge is a knowledge that has high probability of being true , because its veracity has been justified by a reliable method.
The method used to justify scientific knowledge and thus make it reliable, is called scientific method.
When one uses the scientific method to study or investigate nature of the universe, one way is practicing scientific thinking to deduce and analyze something and the other is through observing and experimenting.
REASONING IN SCIENCE
Learning about the scientific method is almost like saying that you are learning how to learn. You see, the scientific method is the way scientists learn and study the world around them. It can be used to study anything from a leaf to a dog to the entire Universe.

The basis of the scientific method is asking questions and then trying to come up with the answers. You could ask, "Why do dogs and cats have hair?" One answer might be that it keeps them warm. BOOM! It's the scientific method in action. (OK, settle down.)
QUESTIONS AND ANSWERS
Just about everything starts with a question. Usually, scientists come up with questions by looking at the world around them. "Hey look! What's that?" See that squiggly thing at the end of the sentence? A question has been born.

So you've got a scientist. When scientists see something they don't understand they have some huge urge to answer questions and discover new things. It's just one of those scientist personality traits. The trick is that you have to be able to offer some evidence that confirms every answer you give. If you can't test your answer, other scientists can't test it to see if you were right or not.

As more questions are asked, scientists work hard and come up with a bunch of answers. Then it is time to organize. One of the cool things about science is that other scientists can learn things from what has already been established. They don't have to go out and test everything again and again. That's what makes science special: it builds on what has been learned before.

This process allows the world to advance, evolve, and grow. All of today's advancements are based on the achievements of scientists who already did great work. Think about it this way: you will never have to show that water (H2O) is made up of one oxygen (O) and two hydrogen (H) atoms. Many scientists before you have confirmed that fact. It will be your job as a new scientist to take that knowledge and use it in your new experiments.
EXPERIMENTAL EVIDENCE
Experimental evidence is what makes all of the observations and answers in science valid (truthful or confirmed). The history of evidence and validations show that the original statements were correct and accurate. It sounds like a simple idea, but it is the basis of all science. Statements must be confirmed with loads of evidence. Enough said.

Scientists start with observations and then make a hypothesis (a guess), and then the fun begins. They must then prove their hypothesis with trials and tests that show why their data and results are correct. They must use controls, which are quantitative (based on values and figures, not emotions). Science needs both ideas (the hypothesis) and facts (the quantitative results) to move forward. Scientists can then examine their data and develop newer ideas. This process will lead to more observation and refinement of hypotheses.
THE WHOLE PROCESS
There are different terms used to describe scientific ideas based on the amount of confirmed experimental evidence.

Hypothesis
- a statement that uses a few observations
- an idea based on observations without experimental evidence
Theory
- uses many observations and has loads of experimental evidence
- can be applied to unrelated facts and new relationships
- flexible enough to be modified if new data/evidence introduced
Law
- stands the test of time, often without change
- experimentally confirmed over and over
- can create true predictions for different situations
- has uniformity and is universal

You may also hear about the term "model." A model is a scientific statement that has some experimental validity or is a scientific concept that is only accurate under limited situations. Models do not work or apply under all situations in all environments. They are not universal ideas like a law or theory