Like how the search engine works, what is caching and indexing, what is sitemaps, and what is crawling. In short start with the basics of SEO.
Learn to search LSI & Long Tail Keywords for website traffic. There are many Tools Like Google Keyword Planner, Semrush Keyword Magic Tool, Ahrefs, ubersuggest.
Read Blogs Like Ahrefs, Moz Blogs, Semrush blogs, watch videos, and listen to podcasts and videos to learn the basics of Link Building, Backlinks, On-Page & Off-Page SEO.
Make a Blog and put your learning into practice, Practice always enhance your skills and for google updates, you can read SEO roundtable blog.
Keeping yourself updated on the latest SEO algorithm updates is a must to stick in this field. Read Blogs like SearchEngineLand and SeachEngineJournel.