How does Canon 600D set the rule of three points?

Find the menu key on the camera and press it;

Then press the left and right keys to find;

When you see "Show Gridlines" on the screen, stop, select and start. As shown in the figure:

One of the simplest rules of composition is the dichotomy. This has become the most commonly used tool for amateur and professional photographers. This method divides the photo into three parts horizontally and vertically, and these nine bisectors and their intersections are the key positions. Trigonometry is a simple and effective rule. For example, landscape photography, the horizon can be placed on the bisector below the horizontal composition. In portrait photography, people's eyes can be located on the last bisector of vertical composition.