Siddhartha's main goal is to discover what is true of the world and to find a life of absolute peace. In other words, he wants to achieve Nirvana. His awakening is not a simply process because it takes him almost his whole life to achieve it. This process of awakening (as his life) is divided into three distinct periods: one which is identified with thoughts, one which is identified with senses and the last one which synthesizes these two into a great unity. Even thought, the starting point of Siddhartha's journey is Hinduism he finds his awakening in the way characteristic for Buddhism. .
We meet Siddhartha when he is dissatisfied with Brahmans( the highest cast in Hindu) because despite their knowledge, the Brahmins are seekers still, performing the same exercises again and again in order to reach Nirvana, which for Hindu is the peace of oneness with Atman the Divine within. However, Siddhartha does not know anyone from them who ever find Nirvana. As Siddhartha says: "One must find the source within one's Self; one must possess it. Everything else was seeking- a detour error" (pg 5).
The young Brahmin finds that if Atman is within then he has to focus on the world within as well. He makes decision to leave the Brahmins.
By joining Samanas he is still continuing his period identified with thoughts. As Samanas, Siddhartha relinquishes all his possession and dedicates himself to meditation, fasting, and other methods of mortification. His goal is to "become empty, to become empty of thirst, of desire, dreams, pleasure and sorrow-to let the Self die."(pg 11). There is a little confusion about which Self Siddhartha is talking. Definitely , he does not talk about Buddhism idea of selfness- AnAtman (at least not yet). In other words, according to the Hindu belief, Self is divided into Atman- that unites individual with other things and into ego which is the result of our consciousness that differentiates an individual from all other things.