Nederland = Netherlands = Pays-bas = Niederland =  official name, meaning 
"low-countries"


Holland, la Hollande etc... common name for the country. Holland was /is 
also a province of the Netherlands.
Part of Benelux, BElgie - NEderland - LUXemburg.


People from the Netherland are and speak Dutch ( NederlandS)

 Germans are / speak Deutsch ( German).

People of Denmark  speak Danish ( Dansk)

People from Belgium speak Vlaams ( Flemish, a form of Dutch with little 
differences in vocabulary and pronounciation), French ( Wallon) and German.

People from Luxemburg speak Letzemburgish ( a form of German), German and 
French


Dutch is spoken in the Netherlands, but its cousin Vlaams ( Flemish, 
Flamand) is spoken in Flanders, reaching throughout Belgium and north-east 
parts of France.
Flanders : an area reaching from the Netherlands to France, across Belgium, 
where people speak a form of Dutch, Vlaams ( Flemish), Bruges, Ghent are 
important cities in this area.
Wallonie : French speaking area in Belgium

does this clear up things ?

Of course these are official languages, there are others, and dialects in 
these countries too