What is a Geth Node and How to Run One

I'v read several articles about geth full sync mode which can be enabled by --syncmode full option But why am I getting error unknown sync mode

A The current default mode of sync for Geth is called fast sync Instead of starting from the genesis block and reprocessing all the

geth fast sync After many many many years, we're sun-setting Geth's fast sync in favor of snap sync #Ethereum

satta king fast 786 chart sync which is more efficient than fast sync and more secure than warp sync Turbo-geth is also used as a platform for the research into Stateless Ethereum