Everything in geometry starts with a single, simple idea: a point. A point isn't a thing you can hold. It has no size, no width, and no depth. It's just a location. Think of it as a single dot on a map marking a specific spot, or a star in the night sky. It marks a position, and that's all.

When you have many points all lined up perfectly, you get a line. A line is a straight path of points that goes on forever in two opposite directions. Like a point, a line has no thickness. It's just length, and that length is infinite. You only need two points to define a unique line. Any two points in the universe can be connected by one, and only one, straight line.

Lines are infinite, but we often work with pieces of them. A line segment is a part of a line with two distinct endpoints. It has a specific, measurable length. A ray is another part of a line. It has one endpoint and extends forever in only one direction, like a beam of light from a flashlight.

Sometimes, points line up neatly. When three or more points lie on the same straight line, they are called collinear points. Think of beads on a straight string. If a point is off that string, it is non-collinear with the others.

We can take this idea a step further. A plane is a flat, two-dimensional surface that extends infinitely. Imagine a perfectly flat, endless sheet of paper. Any points or lines that lie on the same plane are coplanar. It takes at least three non-collinear points to define a unique plane. For example, a three-legged stool is always stable because its three feet are always coplanar.

These are the fundamental pieces of our geometric world. Every complex shape, from a simple triangle to an intricate building, is built from these basic ideas of points, lines, and planes.