The subject of the sentence is simply who or what the sentence is about; it is the reason for the sentence to exist in the first place. For example, in the sentence "Judy ran to school," Judy is the subject; she performs the action and the sentence is built around her. In the sentence, "Films today are not as good as films from 20 years ago," "films" are the subject, as the sentence is about the quality of film.
In English sentences, the subject is often at the beginning of the sentence and is often a noun, but this is not always the case, so make sure to identify the verb in the sentence and then figure out what subject the verb is referring to. Subjects are often nouns or pronouns, though they can also be clauses or phrases.
The verb tells you something about the subject of the sentence and tells the reader the action, emotion or state of being related to the subject. Using the sentences above, you can identify the verbs. In the sentence "Judy ran to school," "ran" is the verb. "Ran" is an action verb, indicating movement. In the sentence, "Films today are not as good as films from 20 years ago," "are" is the verb, which indicates the state of being of "not as good."
Gerunds are verbals -- meaning they derive from verbs -- that end in "ing" and serve as nouns. Because these seem to combine both elements of nouns and verbs, they can often be difficult to identify. Here are some examples of gerunds: "Running is fun," and "Biking to work can be difficult, "The police pulled him over for speeding." In the first two sentences, "running" and "biking" are nouns and also subjects of the sentences. In the third, the word "speeding" is a noun, but not the subject.
In the standard English sentence, the order is subject and verb, as in the sentences "Patty took her daughter to the class," "Harry is a teacher," and "My dog likes to chase cats." Note here that the subject comes first (Patty, Harry and dog) and the verb next (took, is, like). Looking at word order can often help you to identify subjects and verbs in a sentence.