It takes approximately 9.5 volts to start a car. If you hear a clicking sound, your battery is not putting out enough voltage. Your radio, headlights, etc., will all work, so you will think that your problem is your starter. NOT SO. Either you have a weak battery which need charging, or the most likely culprit are your battery cables. Most people will look at their cables and if they LOOK clean, and don't see any white corrosion build up on the terminals, they believe the battery terminals are making a good contact. Once again - NOT SO. Those terminals and cables are lead. Lead is a shiny metal. Scrap the top of a battery terminal and it will shine. That darkness on the terminal you scraped off is also present between you battery terminal and cable, and will prevent a good contact. All it needs is to cause a drop in voltage to your starter and you will hear a clicking sound from the starter.
Get a good battery terminal and cable cleaner at your auto parts store. The type with the wires inside that will really make those terminals and cables shine. Once you have cleaned them, your battery will put out max voltage. If you still hear the clicking sound, take your battery to an auto parts store and they will check it. It may not be holding a charge or you may have a dead cell. However, DO NOT try and clean your battery terminals with Baking Soda or Coca Cola. I've worked on cars for over 55 years and all that does is clean the OUTSIDE of the terminals - NOT the connection between the cable and terminal.
So many people run out and buy a new starter or battery when it is really the connection itself.
Worked on cars for over 55 years.