According to the latest report from Google, around 2500 crore newly discovered web pages are marked as spam. A spammy web page is one which uses shady methods to trick the Googler or provides low quality content. If you want to know whether your content / web page is spammy, you can check here
It is mainly create page for user, not for search engines. Google has a filtering algorithm in place as well as human moderators.
So does this work ? Yes, only 1% of Google users end up on a spammy page. ie, if you have done some funny SEO on your website, the chances are that Google will rank your page low and 99 % of Googlers won't even see your page.
More than 90% of link spam was caught by our systems, and techniques such as paid links or link exchange have been made less effective.
It is time to be careful about link spam. Google now understands link exchange patterns better. According to Google, they are effectively identifying 90 % of the link spam. ie, if you leave a non-relevant link there is a good chance it will backfire on your SEO ambitions.
Google has effectively reduced auto generated and scraped content in 2019 compated to the previous year.