Technical SEO is the method of optimizing the code and delivery of a website or web app for search engine ranking. The purpose of technical seo is to provide a framework for the content seo and general seo to be more effective. Here are some aspects of technical seo:
Index-ability: Ensure the pages are able to be crawled by search engine bots. If bots can’t see the pages then you can’t rank for them. Make sure your site has a sitemap or sitemaps with the right structure to start taking advantage of desktop search, mobile search, image search and more.
Speed: Optimize your website for speed, if people cannot see the site is it really there? 5 seconds or more can knock you down a few notches in search.
Mobile: Mobile and tablets are crucial, if your site isn’t optimized for them you can’t rank well. Remember that the search algorithms are made of many sections and to climb the rankings you must tick off as many of the boxes as possible.
Site Errors: Ensure your site isn’t chalk full of errors, it can kill the rankings. Check your google search console, debug your site using your browsers console feature, and start knocking off any errors you see.
Security: Unsafe sites get flagged quick and it’s hard to climb back up the rankings once your have been infected.
As you can see, this is just a short list of some aspects of technical seo. There are many facets of effective seo (local, content, technical, authority and more), make sure you cover your bases and work on all of them.