What does it mean when you try to start your car and it makes a single click sound but wont start?

Most likely your starter has failed. Old school test: Make sure your battery is good and fully charged. Make sure cable connections to battery are clean and tight. Locate the starter and, depending on access, TAP on the main starter body with a hammer, pipe, long 3/8" extension, broom stick, etc. While someone turns the ignition to the start position. If starter engages and cranks the engine or produces grinding noise and will only barely turn over, the starter is bad. There are other possilble causes, but you gotta start somewhere.