In science you ask a lot of questions, investigate the answers by doing tests (experiments) and report the results of those tests to other scientists. The most important part of asking questions is to have an idea of how things will turn out. This is called a hypothesis.
Think about it: Is it easier to get from home to a store you’ve never seen if someone just gives you a list of directions or if they simply tell you the location of the store? If you have the directions, then you have to think, “OK, I’m at the corner of Euclid and Taylor, and I’m supposed to turn right.” If you have the location of the store, then you can figure it out as you go. Either way, you can get it wrong, but it’s harder to figure out if you only have directions and you take a wrong turn!
When you make a hypothesis, you are essentially saying that you think you know where the store is, and the experiment will be to try and figure out how to get there. If you end up at the wrong store, it could be that your hypothesis was incorrect or that your experiment was done incorrectly. We all make wrong turns sometimes!
The important part about science is that you realize that it is OK – in fact, it’s necessary – to make mistakes. Thomas Edison tried over 700 times to invent the light bulb, but failed each time. Only after those hundreds of experiments did he get it right. When Edison was asked how he felt about making so many mistakes, he said, “I have not failed 700 times. I have not failed once. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.” This means that those 700 ways are actually useful knowledge: Understanding why something does not work the way you think it should will help you understand how it actually works!
Once you have completed the experiment, you need to tell other scientists your hypothesis, how it works (in our example, sharing the directions to get to the store), and the results (data) of your experiment. You can also form a conclusion based on the data. In our example, the conclusion might be: “You need to make two left turns and a right turn in order to get to the store.” If the conclusion is something that is a completely new scientific idea, then other scientists need to test your experiment and get similar results. What this means is that they need to do your experiment exactly as you did it and see if they end up with the same data that you have.
If the experiment is repeated by enough different scientists, and they come up with the same results, then a theory is formed in order to explain what is happening. A theory is different from a hypothesis because it has been tested over and over again, and scientists are pretty sure that it’s true. A hypothesis that has not been tested can not be a theory; a hypothesis that cannot be tested is not scientific! For example, science cannot test to see if God exists, what you are thinking at this exact moment, or if unicorn eyeballs taste salty.