The Buddhist word for enlightenment is "bodhi," which is the basis for the title "Buddha." He was the first to be enlightened and thus was called "The Buddha." The root meaning of bodhi is "to awaken"; thus the Buddha is the "Awakened One." The rest of humanity is asleep.

Enlightenment comes essentially one step before nirvana. It is the realizing of the true nature of the cosmos, the link between samsara and nirvana. It is at this point that one can view their past lives.

Results of the Enlightenment in Gautama:

He got two kind of results: A positive and a negative:
Negatively, the eradication of all greed, hatred and egotism from his mind.
Positively, the cultivation and development of metta, compassion, sympathetic joy and equanimity as inherent aspects of one’s personality. "Metta" is a Pali word and is usually translated into English as "love", and if we simultaneously think of the words "friendship", "love" and "kindness", we will have some understanding of the true meaning of "metta".

With this "Enlightenment", Buddha sought to remove much of the supernatural from Hinduism. Hindus worshiped too many gods, and used too many relics, magic prayers, superstitions, candles, incense... and he saw no need for a church institution or authority or priests or rituals; no need to believe in "miracles" or supernatural agencies as means to obtain "nirvana", after the "enlightenment"... he dared to question the authority of the Vedas and advocated abolishing the caste system... and even suggested that the concept of God be abolished...

How to obtain Enlightenment:

For Gautama it was very simple, he got it "in a flash" under the Bo tree, as we just mentioned.

But it is not so simple... the many traditions, sects, branches and denominations follow different special techniques, most of from Hinduism... and thousands of Buddhist monks and nuns dedicate their whole life with vows of poverty, celibacy, and obedience to try to obtain it.

The Four Noble Truths are the basis to obtain Enlightenment... and most specially Meditation.

Meditation:

In general, to obtain "enlightenment", man's own "mind", "body", and "character", are the greatest obstacles: Please read Meditation and Yoga in Hinduism.. it is the main tool Buddha took from Hinduism... but without gods!...

1-The "mind", is suppressed, for example, by repeating thousands of times a "mantra", a meaningless word for the student, until the "crisis" comes, when the mind gets so boring that stops reasoning, letting only the "animal mind" at work; or by trying to solve for months or years a "koan", an impossible riddle, like "what is the size of your right hand's sixth finger?", until the mind gets so tired, that it gives up, stops reasoning; or trying for months a ridiculous impossible astral projection; or looking for hours at a "yantra", a geometric figure, a triangle...

2- The "body", is restrained by sitting for hours in a difficult position, until numbness occurs... and this way you seek to release the spirit from the limitations of the body, say the Buddhists.

3- The personal "character", is controlled by having a guru or a master that continually humiliates you...

All, until your mind gives up, becomes obsolete, and your body becomes numb, and you feel yourself like nothing, without self, without any personality... and then, "comes the crisis", you will give up your "human mind" and experience the "animal mind" with all kinds of illusory hallucinations and the bliss of having the joy and peace of an animal, without any reasoning, without any concern of yesterday nor today nor tomorrow nor the after death... just the simple instinctive let it go of any animal...

And this is what is called "enlightenment", and "god-realization", and "union with the universal mind", and "heightened awareness", and "cosmic consciousness", and "transcendental bliss"...