According to Oxford Living Dictionaries, to listen is to give attention to sound or action. When listening, one is hearing what others are saying, and trying to understand what it means. The act of listening involves complex affective, cognitive, and behavioral processes. Affective processes include the motivation to listen to others; cognitive processes include attending to, understanding, receiving, and interpreting content and relational messages; and behavioral processes include responding to others with verbal and nonverbal feedback.
Listening differs from obeying. A person who receives and understands information or an instruction, and then chooses not to comply with it or not to agree to it, has listened to the speaker, even though the result is not what the speaker wanted. Listening is a term in which the listener listens to the one who produced the sound to be listened. A Semiotician, Roland Barthes characterized the distinction between listening and hearing."Hearing is a physiological phenomenon; listening is a psychological act."  We are always hearing, most of the time subconsciously. Listening is done by choice. It is the interpretative action taken by someone in order to understand and potentially make meaning of something they hear. 
Alerting, being the first level is the detection of environmental sound cues. This means that certain places has certain sounds associated with them. This is best explained using the example of someone's home. Their home has certain sounds associated with it that makes it familiar and comfortable. An intrusion, a sound that is not familiar (e.g. a squeaking door or floorboard, a breaking window) alerts the dweller of the home to the potential danger.
Deciphering, the second level, describes detecting patterns when interpreting sounds. An example of this level is that of a child waiting for the sound of his mother's return home. In this scenario the child is waiting to pick up on sound cues (e.g. jingling keys, the turn of the doorknob, etc.) that will mark his mother's approach.
Understanding, the third level of listening, means knowing how what one says will affect another. This sort of listening is important in psychoanalysis , the study of the unconscious mind. Barthes states that the psychoanalyst must turn off their judgement while listening to their patient in order to communicate with their patient's unconscious in an unbiased fashion. This is the same way that listeners must turn off their judgment when listening to other.
All of the three levels of listening function within the same plane, and sometimes all at once. Specifically the second and third levels, which overlap vastly, can be intertwined in that obtaining, understanding and deriving meaning are part of the same process. In that the child, upon hearing the doorknob turn (obtaining), can almost automatically assume that someone is at the door (deriving meaning).
Active listening is listening to what someone is saying, and attempting to understand what is being said. It can be described in a lot of ways. Active listening is having good listening skills. The listener is attentive, nonjudgmental, non-interrupting. An active listener analyzers what the speaker is saying for hidden messages, and meanings contained in the verbal communication. An active listener looks for non-verbal messages from the speaker in order to indicate the full meaning of what is being said. With active listening, a person must be willing to hear what someone is saying and the intent to try to understand what the meaning of what the other person said. When active listening is used, there can be multiple benefits. Being an active listener means that you have the possibility to become a more effective listener over time, and your leadership skills will strengthen.
Active listening is an exchange between two or multiple people. When those people are active listeners, the quality of the conversation will be better and more clear. They connect with each other on a deeper level with each other in their conversations. Active listening can create more deep, and positive relationship between the individuals.
Active listening is important in bringing changes in the speaker's perspective. Clinical research and evidence show that active listening is a catalyst in a person's personal growth. The growth is specific with personality change and group development. A person will more likely listen to themselves if someone else is allowing them to speak and get their message across.
Active listening allows for us to be present in a conversation. Listening is a key factor in cultivating relationships because the more we understand the other person, the more connection we create, as taught in nonviolent communication Dharma teachings. As someone recently stated, "we should listen harder than we speak."
Along with speaking, reading, and writing, listening is one of the "four skills" of language learning. All language teaching approaches, except for grammar translation, incorporate a listening component. Some teaching methods, such as total physical response, involve students simply listening and responding.
A distinction is often made between "intensive listening", in which learners attempt to listen with maximum accuracy to a relatively brief sequence of speech, and "extensive listening", in which learners listen to lengthy passages for general comprehension. While intensive listening may be more effective in terms of developing specific aspects of listening ability, extensive listening is more effective in building fluency and maintaining learner motivation.