Holland is the name of a region within the Netherlands (comprised of the provinces of North Holland and South Holland), which is the core area of the country.
Thus, using the term "Holland" for "the Netherlands" is comparable to using "England" for "United Kingdom." In fact, some Dutch object to the use of the term Holland to refer to the whole country (as the Scottish and Welsh night if you used England to refer to the United Kingdom.) Historically, however, Holland was a former county of the Holy Roman Empire.
In English, the people of the Netherlands are called the Dutch. In the Netherlands, they are called Nederlanders.
The language the Dutch speak is also called Dutch in English but called Nederlands in Dutch.
The full name of the Netherlands is the Kingdom of the Netherlands. In Dutch, it is an exact translation (Koninkrijk der Nederlanden). The short form of the Netherlands locally in Dutch is Nederland.
Now you know that, in English, Holland is just a part of the Netherlands and the Dutch are a people and Dutch is a language.