A clause is a group of words, which has a subject and a predicate with a finite verb of its own.
The noun "Arjun" is the subject (doer). "many battles" is the object (the action done) of the verb fought. The subject (doer) may be a noun (Arjun) or a pronoun (we, I, you, he, she, it, they).
To identify the subject ask the question - who. To identify the object ask the question - what.
Clause has a subject, verb, and may be with or without an object. Each clause looks like a sentence but it is not independent. A sentence with more than one clause has:
Main (Principal) clause or Independent clause
Subordinate clause or Dependent clause
An independent clause does not depend on other clauses to make a complete statement. A subordinate clause cannot stand by itself and depends on the main clause to be meaningful.
It is linked with a subordinate sentence connector (that, which, though). Each subordinate clause has a function to perform. Subordinate clause functions as a noun clause or an adjective clause or an adverb clause.
Subordinate clauses are of three types:
Noun clauses function as subject or object, responds to question - Who and What
Adjective Clause qualifies or tells about the subject or object, responds to the question Who and Which
Adverb clause tells about time, place, reason, cause, manner Where, When, Why, How, Because
Subordinate noun clauses function as object. The noun clause does the same function in a complex sentence which a noun or pronoun does in a simple sentence.
1. Rajesh informed the visitor that the admission notice has been published in the newspaper.
2. My friend, who was coming from Mumbai, has postponed his visit.
3. Yogesh cannot take the final exam because he is unwell.