I think that 'rebirth' is not the most important topic in Buddhism; but it is the topic which I thought I understood the least, and so it was the first topic which I asked about:
Is rebirth a delusional belief?
It was later, in answering this question, that I hope I came to satisfactory understanding of the anatta doctrine:
How is it wrong to believe that a self exists, or that it doesn't?
Furthermore, this answer includes an attempt to summarize "What's the value or harm of a literal belief in rebirth?" -- but I don't know any better short summary than this comment ...
it's not that Buddhists believe in rebirth, it's that we don't believe in death
from the same answer; or than the folk-singer's doctrine which was summarized in this answer.
Step by step
The OP posted a comment to give an example of what he meant by "step by step".
Another way to sequence (doctrine and practice) might be the so-called Threefold Training.
And, you might like to consider this list of Useful resources suggested by the users of this site.
But (apart from those) I posted some questions about the Four stages of enlightenment of Theravada Buddhism.
If I recommend the following, it's not that mine were good questions (I didn't know what I was asking about, maybe it's not useful to read the questions) but you may find the answers to these topics helpful:
- What are examples of identity-view?
- How are 'conceit' and 'identity-view' not the same?
If you go to a bookstore and look for books about Buddhism, it's easy to find many books written by modern authors.
In studying a religion, in the past I have often wanted to try to read the "original" doctrine and not only the more modern interpretations (if I were studying Christianity, for example, I would prefer to read the red words in the Gospels than to read anything else).
Anyway, I took advantage of this site to ask two other questions, about access to that literature:
- English (or other European) translations of Pali Canon
- Chronological or other sequence for beginners
Other forms/schools of Buddhism
I find it, unfortunately, difficult to even ask sensible questions about other forms of Buddhism (I hope that other people may so that I can read the questions and the answers).
I recommend or remember the following as having given me some insight into at least the existence of forms (doctrines, practices, traditions) of Buddhism in addition to the Theravada of the Pali canon:
- How to explain what Buddhism is?
- What is meant by Namu Amida Butsu and also Nam-myoho-renge-kyo?
- Pāramitāyāna and Tantrayāna