Dutch is the adjective that goes with one country, the Netherlands. The country name and the adjective do not look alike, so it helps to learn them as a pair. You can put Dutch in front of almost anything that belongs to that country: a Dutch city, Dutch cheese, a Dutch friend, Dutch history. It also covers the language, so a Dutch class is a class in that language. The D stays capital wherever the word sits in the sentence.

As a noun, Dutch is the name of a language. It is uncountable, so it takes no a and no plural. You speak Dutch, you learn Dutch, and something is written in Dutch. Watch the little word the here: in Dutch means in that language, but the Dutch means the people of the Netherlands. Belgium has more than one language, and Dutch is used in part of it, so a Dutch speaker is not always from the Netherlands.