new to this - what is topical authority?

it just means google trusts you on a subject because you've covered it properly, not with one post. so instead of a single 'guide to x', you have the main page plus the smaller questions people actually ask around it, all linking to each other. at a small scale it matters more, not less. you can't win on links, so being the site that answers every angle of one narrow topic is the realistic way in. pick one topic, cover it fully, then move on to the next.