Centripetal forces are forces that pull something in, causing it to orbit.
Earth is forced to orbit the sun because of the centripetal force the sun has. If this force wasn't there, earth would more off into space. The centripetal force that makes the earth orbit the sun is only there because of the gravity between the earth and the sun. The same applies for the moon and earth; the moon orbits earth because of the centripetal force between them.
This is the direction in which the thing orbiting wants to move, and the direction in which the centripetal force makes it move. They are always at right angles.
...that the angle the earth wants accelerate at is at a right angle to the direction it is being pulled by the sun.
These orbit with the earth, and therefore stay over the same point of the earth at all times.
LOW POLAR ORBIT SATELLITES
These pass over both of the earths poles, as the earth rotates beneath it.
Microwaves are used for satellite communication, and so have higher frequencies.