What does it mean that a planet sweeps equal areas in equal time?
Similarly, you may ask, why do you think the area swept out by a planet in a given period of time remains constant?
The area the planet sweeps over is equal because when it speeds up the length covered along the orbital path is greater, but it is also closer to the star, and that dimension is decreased.
Then, what is meant by Kepler's second law which states that as a planet moves around its orbit it sweeps out equal areas in equal times?
Kepler's second law states that a planet moves in its ellipse so that the line between it and the Sun placed at a focus sweeps out equal areas in equal times.
Kepler's first law - sometimes referred to as the law of ellipses - explains that planets are orbiting the sun in a path described as an ellipse. The resulting shape will be an ellipse. An ellipse is a special curve in which the sum of the distances from every point on the curve to two other points is a constant.