You're asking the right person...
I'm head of SEO for PhobbMedia.com
It's a super rewarding field, but not one that you can learn overnight or with low effort.
If your looking to get results asap, I'd suggest just hiring professionals.
When you take into account the value of your time and the knock on effect of lost earnings while you get up to speed... It's actually cheaper to hire professionals than doing it yourself.
That said, if you have a passion for it, and are willing to devote hundreds of hours learning it.. it can be one of the most valuable skills you can learn.
Other high value skills include copyrighting, public speaking, sales/closing, social media, content creation, and networking. Learning leadership, outsourcing, automation, systems, process optimization, and project management won't hurt either.
As for a starting point... I maintain a list of the top SEO related blogs so that I can stay current and also invest thousands every year on my education. I'm sure you can start off on the cheap though.
Check out Udemy.com for some super cheap SEO courses. They run regular $10 and $20 specials, and there might even be some free courses.
Also a good start:
https://neilpatel.com/what-is-seo
https://backlinko.com/google-ranking-factors
https://moz.com/beginners-guide-to-seo
https://blog.feedspot.com/seo_blogs