What do the es-, the levo-, and the dex- mean in drug names?

Psychopharmacologists come across the terms levo- or dextro-, es-, dex-, dextro-, enantiomers, isomers, racemic, etc.  What do these terms mean? For example, what is the difference between: Escitalopram (Lexapro®) and citalopram (Celexa®)? Levomilnacipran (Fetzima®) and milnacipran (Savella®)? Dexmethylphenidate (Focalin®) and methylphenidate (Ritalin ®)? Dexamphetamine (Dexedrine®) and amphetamine? Eszopiclone (Lunesta®) and zopiclone? We are clinicians and don’t…