What is the difference between Automatic transmission and Manual transmission?

Automatic transmission have only few select options, like forward, neutral and reverse. Where manual transmission will have complete gear selector.
For buyers, Automatic means a vehicle will select a appropriate Gear by itself as 1st, 2nd or .... as per the vehicle speed and load. where in Manual a driver has to decide and put vehicle in correct gear to move in desired form.
Automatic may have solenoid gear selector or a complex mechanism of overdrive and clutches which we see in luxurious vehicles only.