Once you know in which direction the object is located, you need to know how high in the sky to look for it. That's where Altitude comes in.Altitude ranges from 0 to 90 degrees, and measures the angle between the horizon, you, and the object. An object with 0 degrees altitude is right on the horizon, while an object at 90 degrees altitude is directly overhead. If you stretch out your arm and make a fist, then your fist covers about 10 degrees on your field of vision, so if the sun is at 40 degrees altitude, it is about 4 outstretched fists above the horizon.
Occasionally, you will see altitudes less than zero, e.g. "At 9:30 PM, the sun will be at -20 degrees altitude." In this case, the sun would be 20 degrees below the horizon, you would be unable to see it, and it would be night time.