Read the passage first:
A day laborer is an individual who does heavy manual labor in fields. As he does manual works, he is to be healthy, strong, and stout.
If he gets more work, he earns more. If he cannot manage work, he and his family go without food.
The first sentence in the above passage has two clauses (i) A day laborer is an individual and (ii) who does heavy manual labor in fields. Both the clauses contain a subject and a finite verb. The first clause gives a complete sense; whereas the second clause has a subject who and a verb does depend on the first clause to give a complete sense. Hence, the first clause a day laborer is a person is a principal clause and the second clause who does heavy manual labor in various fields is the subordinate clause. The other sentences of the passage also consist of principal and subordinate clauses. A clause may also form a sentence.
Example: He arrived late, (one clause sentence)
Clauses:
A clause is a set of words that includes at least a subject and a finite verb. A clause can be a complete sentence or just a portion of a sentence.
Clauses are of three types:
(1) Independent or Principal or Main Clause
(2) Dependent or Subordinate Clause
(3) Co-ordinate Clause