VERBS

The shortest sentence contains a verb. You can make a one-word sentence with a verb, for example: "Stop!" You cannot make a one-word sentence with any other type of word.
Verbs are sometimes described as "action words". This is partly true. Many verbs give the idea of action, of "doing" something. For example, words like run, fight, do and work all convey action.
But some verbs do not give the idea of action; they give the idea of existence, of state, of "being". For example, verbs like be, exist, seem and belong all convey state.

A verb always has a subject. (In the sentence "Joe speaks English", Joe is the subject and speaks is the verb.) In simple terms, therefore, we can say that verbs are words that tell us what a subject does or is; they describe:
action (Ramasamy plays football.)
state (Andy seems kind.)

There is something very special about verbs in English. Most other words (adjectives, adverbs, prepositions etc) do not change in form (although nouns can have singular and plural forms). But almost all verbs change in form. For example, the verb to work has five forms:
to work, work, works, worked, working

Source:http://www.englishclub.com/grammar/verbs.htm