Sun — the sign most people mean by "your sign." It's worked out from your date of birth alone, and it tends to describe the core of how you move through things.

Moon — how you feel, privately. It changes sign roughly every two and a half days, so it needs a birth time to place accurately, and it often shows a side of you that only people close to you see.

Rising — how you tend to come across, especially at first. It changes sign about every two hours, so it needs the most precise birth time of the three, and an unclear time will usually leave it unreliable.