How does it work?
Localizer at the far end of the runway (so aircraft on auto-land can use it to stay on the runway in zero visibility) transmits two lobes at different modulations on your selected frequency. Your aircraft's reciever interprets what it detects of the two signals and displays it as a "fly right / fly left" indication.
Glide slope aerial also transmits two lobes but on a paired frequency in the 300MHz range. Your receiver knows automatically which frequency is paired with the selected localizer frequency. It interprets the two signals to give you a "fly up / fly down" indication.
The shape of the lobes mean that you are funnelled onto the runway (so close in, a small deviation will move the indicator a long way).
There is a technical limitation / gotcha (which you would be trained for on an instrument course) in that the lobes can be picked up incorrectly if you are too high - so instead of going down at 3 degrees, if you follow them you would descend at a much steeper angle - so the training is especially important! A few airliners have come to grief that way.
HTH