Motivation

Motivation is an important part of psychology. It is the driving force by which people (or animals) get what they want. A motive is the reason for an action taken.
Motivation arouses a person to act towards a desired goal. It is a driving force which promotes action. For example, hunger is a motivation which causes a desire to eat. "Motivation is an energizer of behavior". It is the purpose or psychological cause of an action.
With animals, motivation is caused by basic needs: needs for food, water, warmth, safety, mating, protecting the young, defending territory, needs to escape pain and threats... The drive to do these things is instinctive, inborn, and triggered by circumstance.
With humans, whose mental life is much more complex, motivation is more complicated. Obviously, humans feel the need for food and water, avoid pain and so on. But they are also capable of having long-term plans which are more difficult to understand.
Drives.
A drive or desire is "a deficiency or need that activates behaviour aimed at a goal or an incentive".&lt;ref name="Drive/Desire"&gt;&lt;/ref&gt;
Drives may arise inside or outside an organism. External drives for humans are rewards and punishments, and can be quite subtle: a frown or a smile may be sufficient for a young person.
Drives often occur "within" the individual and may not need external stimuli to encourage the behaviour. An example is the sexual drive which is driven by our hormone system. The desire for sex is wired deep into the brain of all human beings as glands secrete hormones that travel through the blood to the brain and stimulates the onset of sexual desire. The process is started by the brain's hypothalamus, which releases pulses of GnRH (gonadotropin-releasing hormone). This starts a whole chain of reactions which we call "puberty". Longer term, the hormone supporting male sex drive is testosterone, and for women testosterone and oestrogen.
By contrast, outside rewards and stimuli are used in training animals by giving them treats when they perform a trick correctly. The treat motivates the animals to perform the trick consistently, even later when the treat is removed from the process. Children are motivated to learn by approval of friendly adults, and by their own pleasure at success.
Emotions and unconscious motivation.
Motivation and emotion are intertwined: "Emotional states tend to have motivational properties".
Not all motivated behaviour is the result of conscious decisions. Freudian psychology suggests that much behaviour is motivated by "unconscious factors, working through a network of defence mechanisms, symbolic disguises and psychological cloaks".
References.
5. Motivation is the world of energy, power and positive vibes.