The sun is shining today. Why is it daytime where you are right now?
It is daytime because the part of Earth you are standing on is currently turned toward the Sun. Earth is a spinning ball: it rotates once on its axis about every 24 hours. The half facing the Sun is lit, and we call that day; the half turned away sits in Earth’s own shadow, and we call that night.
The Sun does not really travel across your sky. It looks like it rises and sets, but that motion is the ground beneath you turning. Sunrise is the moment your horizon rotates into the sunlight; sunset is the moment it turns back out of it.