"La neta" is the truth, or what you say when you're about to be honest, like "to be honest". "Neta" on its own is like "for real", and if you ask "¿neta?" you want to know if something is true.
La neta no me gustó la peli. —¿Neta? A mí me encantó.
"La neta" I didn't like the movie. —"¿Neta?" I loved it.
It's when something is really nice, pretty, or you just love it. You use it for things that look good, are well made, or that you have a great time with.
Qué chido estuvo el concierto de anoche, ¡hay que repetirlo!
How "chido" last night's concert was, we have to do it again!
