In one sentence, describe what the following article is about:

It is important that you carefully follow all of the instructions provided in order to receive accurate results. For example, during the test you will likely be asked to cover one of your eyes with your hand and then answer a variety of questions. You will then be asked to cover your other eye and answer another set of questions. This is done in order to test the vision in each of your eyes. You may be asked to leave your glasses on if you already wear glasses to help with your vision. When taking a visual acuity test, an "E" will appear on your screen and you will be asked to select the arrow that the open side of the "E" is facing. The "E" will rotate and change sizes as you complete the test. Depending on the website you are using you may be asked to cover one eye and take the test and then repeat the questions with your other eye covered. An online vision test that looks at your ability to see contrast can also help determine if you need corrective lenses. To complete this test, a "C" will appear on your screen and you will be asked to select the arrow that the open side of the "C" is facing. As you complete the test the "C" will rotate and the darkness of the letter will change. For example, in some instances the letter will be very dark and easy to read and at other points it will be so light that it will become difficult to see against the white background. A colour vision test will check to see if you can distinguish different colour contrasts, most notably red, green, and blue. These tests vary slightly, but in most cases a circle will appear that is filled with different coloured circles. You will then be asked to read the number that is hidden inside the circle. If you are not colour blind you should be able to see the numbers easily based on the contrasting colours. An online astigmatism test will ask you to cover one eye and look at a series of lines. You will be asked if some of the lines appear darker than others. Then you will then be asked to cover your other eye and determine if some of the lines are darker than others. You should only see darker colours with one of your eyes, not both. If this happens you may have astigmatism and should talk with your eye doctor. At the end of each test you will be given your results. You may receive excellent results for each test. This indicates that your vision is good and you likely do not need glasses. For some tests, you may receive a poor result. When this happens the site will recommend that you see an eye care professional in order to receive a full eye exam. Some sites will only provide you with results after you have provided your email address and name.

Summary:
Follow the instructions. Test your visual acuity. Take a contrast vision test. Try a colour vision test. Take a test that measures astigmatism. Read your results.