Ryder Carroll just released his book The Bullet Journal Method in October 2018. Highly recommend giving it a skim; it's a highly opinionated template about where to start with Bullet Journaling (kind of like Ruby on Rails or React for Bullet Journaling).
That said, if you are just getting started, it's way too easy to fall in the trap of setting up the tool instead of actually being productive. You want to fail cheaply and quickly: I'd recommend starting with unstructured paper (loose-leaf paper or a memo pad or whatever is handy) and doing just rapid logging for two or three days to see if you find it helpful. (The list of bullets can be found at https://bulletjournal.com/pages/learn) If you find that helpful, then you can dig deeper with buying the book and/or buying a notebook.
Yeah, that's a problem/trap I fall into a lot with any sort of productivity aid. Omnifocus was a nightmare for me. I never did finish tweaking it to be just "right" because I really didn't know what "right" was.
I tried with OF for a long time, but I never got it quite right - plus, mobile capture seemed needlessly slow and fiddly, and then they rev'd the tool to include WAY more white space and WAY less information density, and that was it for me.
I ended up in OrgMode, of all places, which is kind of funny since I wasn't really an emacs person before. Obviously, I am now.
I trust it in a way I don't think I ever really trusted OF, and I find myself using it much more consistently and religiously. It's been really good for me.
OmniFocus is really productive for me. I am also periodically changing how I use it, but the difference is that I do that while I am using it to get work done so the changes are legitimate optimizations of a working system. I think it defaults to a good outlined task list tool for indecisive people. I think the trap it sets is getting Pro too early; trying to set up custom perspectives before using it enough to understand what perspectives would save time is counter-productive. Setting up a dense thicket of tags is also a mistake, I suppose.
it makes sense. Modular, as in composed of discrete modules that can be combined. Framework, as in it provides a structure and library that you use to assemble your own version. Sure it's a bit software-y but I'm assuming that's the creator's background.
That said, if you are just getting started, it's way too easy to fall in the trap of setting up the tool instead of actually being productive. You want to fail cheaply and quickly: I'd recommend starting with unstructured paper (loose-leaf paper or a memo pad or whatever is handy) and doing just rapid logging for two or three days to see if you find it helpful. (The list of bullets can be found at https://bulletjournal.com/pages/learn) If you find that helpful, then you can dig deeper with buying the book and/or buying a notebook.