An adjective clause, like a noun clause, is always a dependent clause. Like an adjective, the adjective clause describes a noun.  Since a noun can be a subject or an object, an adjective clause will modify subjects and objects. What makes is a clause is that it is formed by a collection of words, two or more, one of which is an adjective, and which describes a noun. An adjective clause, also called an adjectival or relative clause, contains and noun and a verb.

examples of the adjective clause

Here is a simple sentence with an adjective:
“This is an unfinished carving.”  The adjective in this sentence is ‘unfinished’.  It is an adjective because it describes a noun with one word.
If we decide instead to write the sentence thus:
“This is a carving, which is unfinished.”  This becomes an adjective clause, because, although it is still dong the job of describing the noun, but it is doing so using more than one word

Other adjective clause examples:
Sadie, who is a fine linguist, teaches English. Adjective clause modifies the subject, Sadie.
We are going to a party, which begins at dusk. Adjective clause modifies the object, a party.

Note that the adjective clause  n the two above sentences is introduced by the relative pronouns, ‘who’ and ‘which’.  This is a hard rule for this clause – and there is a set of relative pronouns, easy to remember, which always introduce the clause.  They are who, whom, whose, which and that.
This clause, like a noun clause, is always a dependent clause. Like an adjective, the adjective clause describes a noun.  Since a noun can be a subject or an object, an adjective clause will modify subjects and objects. What makes it a clause is that it is formed by a collection of words, two or more, one of which is an adjective, and which describes a noun.