がある + (Noun)Noun (B) that has Noun (A), Noun (B) with Noun (A)

In this expression, がある has the role of describing the noun that follows it. The description that it is giving is '(A) がある (B)' = '(B) has/with (A)'. This type of phrase is called a relative clause (something that describes a noun), and behaves similarly to an adjective.

In English, a relative clause would require a pronoun such as 'who' 誰(だれ), 'which' どれ, 'that' それ・あれ, 'where' どこ. However, these types of words are not required in Japanese, and the noun will follow がある directly.

Caution

In a relative clause, because (A) is describing (B), (B) will be considered the 'main topic/subject'. This means that は will generally not be used in place of が. However, の can be used instead of が, as showing a relationship between (A) and (B) is one of the main functions of の.