Hi Rowanblake, welcome!
I got started on my publishing journey not that long ago, and I remember the feeling of being utterly overwhelmed by everything - all the terminology, the options, the different opinions. Yikes!
A really simple thing that helped me was to get a notebook (I do like old fashioned pen and paper sometimes) and basically make a list of what I thought was involved in publishing an e-book and what I needed to know. For example: covers, editing, formatting, KU or wide. I added to the list as I went.
Then I tackled each subject one at a time. For example, I spent a while looking at cover options, hunting down designers I liked, looking at covers in my genre, etc, etc. Then moved on to the next thing. That worked for me as I wasn't trying to do everything at once!
For me, I decided to hold back publishing my first book until I had the first three nearly done (although that plan went a bit wrong - book 3 took longer than I'd planned!). I also published exclusively with Amazon, in KU for several reasons, not least that, as I'm just starting out, it only gives me one platform to learn and get familiar with to start with.
Best of luck.