I am not a practicing Buddhist. In the past say two years I have done some (non-extensive) research of Buddhism however and I have come to appreciate many of its principles.

Siddhārtha Gautama was born in 623 BC at the foot of the Himalaya as the son of King Suddhodana and Queen Maha Maya. Being a prince, Siddhārtha lived a life of luxury and got the best education available. In spite of all this luxury and wealth he felt there had to be more, so he left his family and belongings behind and chose an ascetic life. He became the student of two hermits, Alara Kalama and Udaka Ramaputta, but still did not succeed in his quest: finding the cure against suffering.

He sat down under a pipal tree, now known as the Bodhi tree in Bodh Gaya and vowed to remain there until he had found the truth. After 49 days of meditation he attained enlightenment. From that moment on he was known as the Buddha (Awakened One).

Buddha spent the rest of his life traveling and teaching his principles, known as Majjhima Patipada, the path of moderation. This path is based on virtuousness (sila), concentration (samadhi) and wisdom (pañña).

The noble truth of suffering

"Now this ... is the noble truth of suffering: birth is suffering, aging is suffering, illness is suffering, death is suffering; sorrow, lamentation, pain, grief and despair are suffering; union with what is displeasing is suffering; separation from what is pleasing is suffering; not to get what one wants is suffering; in brief, the five aggregates subject to clinging are suffering."

The noble truth of the origin of suffering

"Now this ... is the noble truth of the origin of suffering: it is this craving which leads to renewed existence, accompanied by delight and lust, seeking delight here and there, that is, craving for sensual pleasures, craving for existence, craving for extermination."

The noble truth of the cessation of suffering

"Now this ... is the noble truth of the cessation of suffering: it is the remainderless fading away and cessation of that same craving, the giving up and relinquishing of it, freedom from it, non-reliance on it."

The noble truth of the path that leads to the cessation of suffering

"Now this ... is the noble truth of the way leading to the cessation of suffering: it is the Noble Eightfold Path; that is, right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, right concentration."

For me, this is why I appreciate Buddhism. Buddhism does not put some divine entity in charge. You yourself are responsible for your life. For me, becoming a Buddhist starts here, with the Noble Eightfold path. I am yet to be convinced of reincarnations and one cosmic spirit. I don't reject them, but I don't believe in them either. What I do believe is that you become what you think. By this I am not saying that if you think hard enough you can and will become anything you want to become. One has to be realistic. But it all starts with what you think, how you think, how you perceive yourself and the world around you. I have experienced that changing your mindset to a positive one causes the people and the world around you to change. If you act and speak with the right intentions, effort, etc - in other words: if you practice the Noble Eightfold Path - people will react accordingly and things will change.

The Noble Eightfold Path is sometimes divided into three basic divisions. The three basic divisions are as follows:

Wisdom (Sanskrit: prajñā, Pāli: paññā)

Right view, by which you acquire Right knowledge.

One should be aware that everything, literally everything is a matter of perception and everything is transient. Anything that has a beginning will also have an ending.

Right intention, by which you acquire Right liberation.

The right intentions are free of lust, free of bad motives and free of vexatiousness.

Ethical conduct (Sanskrit: śīla, Pāli: sīla)

Right speech.

Right speech is truthful, not slandering, free from harsh words and sensible.

Right action.

Right action involves not killing, not taking what has not been given and not indulging in (sexual) misconduct.

Right livelihood.

You should provide in your needs in an honorable manner.

Concentration (Sanskrit and Pāli: samādhi)

Right effort.

Be aware of and fight the evil inside yourself and be aware of and foster the good in yourself.

Right mindfulness.

Remember (to nourish and take care of) your body, your emotions, your mind and mental objects.

Right concentration.

Meditate and develop your vision and insight.

As with most large religions there are several movements within Buddhism. I couldn't recommend a certain school, as I don't know the differences, but I'd advise you to do your own research and find out what appeals most to you. If you really want to become a practicing Buddhist, then I think you will want to find teachers. The path to Enlightenment is through meditation, but there probably is more to it. How to become a Buddhist is up to you, you must find your own path. After all, it was Buddha who said:

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense.