1) The essential parts of a noun group A noun group consists or at least the following elements: a determiner and a noun. 2) Other parts of a noun group. A noun group can also contain one or more modifiers; a modifier is an adjective, an adjectival phrase, a secondary noun, a prepositional phrase or a relative clause. The principal noun in a noun group is called the head noun. Check this site: http://linguapress.com/grammar/grammar3.htm I hope it helps.

Nouns, of course. It can be modified by an adjective or another noun. Here's an example: A boy and his younger brother were playing a ball. A noun phrase here is 'a boy and his yonger brother'.