A clause is two or more related words that work together that contain a subject and a verb.
There are two types of clauses- independent clauses (which can stand alone as a sentence) and dependant clauses (which can not stand alone as a complete sentence because they do no convey a complete thought).
Although she was intelligent (dependent clause- does not convey a complete thought)
Elephants consume large amounts of food. (independent clause- can stand alone)
There are three kinds of dependent clauses: relative clauses, adverb clauses and noun clauses
This is a dependent clause that acts as an adjective- so it describes or gives more information about a noun or pronoun. A relative clause follows the noun or pronoun it modifies and begins with a relative pronoun.
Marty, who works in my office, is a great ball room dancer.
XXX(the clause gives more information about Marty)
An adverb clause is a dependent clause that starts with a subordinating conjunction. Adverb clauses function as adverbs and modify verbs, adjectives, or other adverbs in an independent clause. Adverb clasues tell when, where, why, how, how long, or how far.
After Kelly fied her car, she drove to San Diego all by herself.
XXX(the clause answers the question when she drove)
A noun clause is a dependent clause that functions as a noun and usually begin with a relative pronoun.
Percy told his wife that the baby was already asleep.
XXX(the clause functions as an object of the verb told)
For more information about clauses take a look at
An explanation of the different kinds of clauses in English and their function: relative clause, noun clause and adjective clause– www.understandinggrammar.com