What is the difference between regular advertising and SEO promotion? How to understand what is better specifically for my site? Help me understand all the subtleties
I completely agree that you have to go to a professional for answers. One book or article is not enough. They will audit your site, analyze the main competitors in the niche and explain what work is to be done. Maybe there will be something you won't agree with and you won't want to continue working with them. Maybe your niche doesn't have competitors at your level and you don't need SEO promotion. Again, all the answers need to seek the professionals. I would advise SEO company "To-The-TOP!" , simply because I'm working with them for more than a month, and I see concrete results.
In order to understand the intricacies of SEO you need to start studying the topic comprehensively and from the beginning. It's not enough a simple answer in one sentence. So you have two options - to learn yourself or pay a professional for a full audit. Here everyone decides for himself, depending on the availability of free time and money.