Hey @artur-foodamigosi! It all depends on how you've configured the site. Redirects, robots.txt options, canonical links, site content, and many other factors affect SEO outcomes.

To get a better understanding of how to configure your site for better results, I recommend using Google's SEO Starter Guide. There's a ton of useful information in the guide. Be sure to dig into the sub-pages.

I know what factors boost up a sites seo and that seo has many factors that it considers. But I simply want to confirm that if i apply good seo rules on my mircosite, that it is embeded under a primary domain, that google treats this microsite as part of the primary domain.

I don't have a simple "yes" or "no" answer for this. It really depends on too many factors, including how your sites and domains are configured.

Google's SEO guide claims that subdomains versus subdirectories is something they believe you shouldn't focus on.

From a business point of view, do whatever makes sense for your business. For example, it might be easier to manage the site if it's segmented by subdirectories, but other times it might make sense to partition topics into subdomains, depending on your site's topic or industry.

You can also check the resources from Yahoo, Bing, Yandex, and other search engines. It may be worth hiring and SEO professional if you feel your site is in need of review or enhancement in that regard.