ILS & Glide Slope
Instrument Landing System, or ILS, is used by pilots to steer them directly to the runway on the last leg of flight. An array of antennas send out a phased signal that causes a needle in the cockpit to swing left or right. When the needle is centered, the pilot knows he is lined up directly with the runway. He can line up with the runway as soon as he is in range of the ILS. A lock can be had from many miles away. This takes care of being lined up left & right of the runway. How can you land at night or in adverse weather, when you don't know if you are landing too soon or overflying the runway? Another needle reading called Glide Slope.
Glide Slope puts out a straight line signal to distant aircraft. Imagine shining a light beam from the end of the runway to the aircraft. If the aircraft follows the beam exactly, he will descend in a straight line & wind up at the base of the runway. Glide Slope puts out a radio "beam" to the Glide Slope receiver in the planes. No matter what altitude the plane is flying, the pilot only has to look at the Glide Slope indicator during descent. If the needle is over the center line, he is over the "beam." He knows he is too high to fly in at a straight line and must descend until the needle is centered. If it is under the center mark, he knows he has to ascend. All the way down he must cross-check the Glide Slope readings and the ILS readings. This will ensure his arrival exactly at the base of the runway, centered left/right and vertically.
No matter what visiblity conditions exist, the plane can take off and land completely by instruments. Pilots can look at the instruments & fly by needle and/or digital readouts. Or the plane can fly itself with autopilot, using computers to keep the plane centered on the beams.
I'm no rocket scientist, but this is a good basic course of how airplanes can fly by themselves, or bad visibility. Scope your local library for more info.