The Pali scriptures are mostly consistent; without contradiction. The primary themes are non-harming (morality), non-sensual happiness (concentration) & non-attachment (wisdom).
However, there are certainly some notable contradictions in them (for example, the Maha-Nidana Sutta), which I speculate were later attempts to introduce ideas about 'reincarnation' into the scriptures so a 'social religion' attracting a broader audience could be developed.
I would speculate this ultimately lead to the demise of Buddhism in India, making Buddhism indifferentiatible from Hinduism.
The foundation for a proper understanding of the Pali teachings is to embrace the principle that is chanted everyday in Theravada Buddhist countries about the Dhamma or Teachings, namely:
Svākkhāto Bhagavatā dhammo, sandiṭṭhiko, akāliko, ehipassiko, opaneyyiko paccattaṃ veditabbo viññūhī ’ti.
Well taught is the Dhamma of the Blessed One, visible here and now, not involving time, inviting investigation, leading onwards, to be
experienced by the wise.
If a doctrine is believed or adhered to that cannot be experienced in the here & now by an ordinary mind, this is not the original doctrine.
Therefore, any translations of the Pali Canon that do not make sense to the ordinary reader are not the original doctrine (since the Dhamma is 'well taught', plain & straightforward, as stated in the scriptures).
The greatest problem is that of language & translations. There are many crucial translated words, such as 'birth', 'death', 'cessation', 'body', etc, which are interpreted in ways that result in not being able to experience the interpretation in the here & now.
Fortunately, all of these crucial words are well-defined in the scriptures therefore those searching for a meaning that can be 'experienced in the here-&-now' can find it.
If you want to read something for beginners that accords with my explanation above, these links:
Two Kinds of Language
Buddha-Dhamma For Students