A horizon is that line at which the sky meets the earth when you look out into the distance. This definition applies so much in landscape photography where the aim is to maintain a level horizon. There are a few tools that you can use ensure the horizon is level. One is to put a small level on your camera to help keep the horizons straight. How do you achieve this? You can either correct the tripod legs or the tripod head and make small adjustments or use gear heads to make tiny adjustments

At the four intersecting points

Rule of thirds in photography involves mentally dividing up a scene or an object of interest into two horizontal and two vertical lines. The result is 4 intersection points. You then position a subject at the points where these lines meet. Your photograph will have the best composition when you follow this rule.