Verbs carry the idea of being or action in the sentence.
Verbs are classified in many ways. First, some verbs require an object to complete their meaning: "She gave _____ ?" Gave what? She gave money to the church. These verbs are called transitive. Verbs that are intransitive do not require objects: "The building collapsed." In English, you cannot tell the difference between a transitive and intransitive verb by its form; you have to see how the verb is functioning within the sentence. In fact, a verb can be both transitive and intransitive: "The monster collapsed the building by sitting on it."
Helping verbs or auxiliary verbs such as will, shall, may, might, can, could, must, ought to, should, would, used to, need are used in conjunction with main verbs to express shades of time and mood. The combination of helping verbs with main verbs creates what are called verb phrases or verb strings. In the following sentence, "will have been" are helping or auxiliary verbs and "studying" is the main verb; the whole verb string is underlined:
A linking verb connects a subject and its complement. Sometimes called copulas, linking verbs are often forms of the verb to be, but are sometimes verbs related to the five senses (look, sound, smell, feel, taste) and sometimes verbs that somehow reflect a state of being (appear, seem, become, grow, turn, prove, remain). What follows the linking verb will be either a noun complement or an adjective complement:
Verbs are also said to be either active (The executive committee approved the new policy) or passive (The new policy was approved by the executive committee) in voice. In the active voice, the subject and verb relationship is straightforward: the subject is a be-er or a do-er and the verb moves the sentence along. In the passive voice, the subject of the sentence is neither a do-er or a be-er, but is acted upon by some other agent or by something unnamed (The new policy was approved).