BASICS 

All sentences in English language include two parts: the subject and the verb (this is also known as the predicate). The subject is the person or thing that does something or that is described in the sentence. The verb is the action the person or thing takes or the description of the person or thing. If a sentence doesn’t have a subject and a verb, it is not a complete sentence. For example, in the sentence “Went to bed,” we don’t know who went to bed.

 SUBJECTS 

All verbs have a subject. The subject is generally the person or thing that the sentence is about. It’s often the person or thing that performs the action of the verb in question and it usually (but not always) comes before the verb. A Subject can be a noun, noun phrase, or a noun clause. A noun is a word (other than a pronoun) used to identify any of a class of people, places, or things (common noun), or to name a particular one of these (proper noun). A noun phrase is a word or group of words containing a noun and functioning in a sentence as subject, object, or prepositional object. A noun clause is a clause that plays the role of a noun. 

Trolls were looking for the loo.

The trolls from the neighborhood were looking for the loo.

What the trolls were looking for was the loo.