In this hangout, this webmaster was concerned about links and asked John Mueller what his advice was for getting them. John also explained a few things regarding bad links.
John explained that problems occur when one goes out and creates the links themselves. The entire idea behind link building is to allow others to build links back to your site and that this happens naturally.
But, if Google finds that you’re building these links back to your site, this could be a major problem and may result in a penalty, for example.
However, the usual processes of creating great content—spreading the word about that content, getting influencers, and getting them to write about your site—are all perfectly fine.
Just don’t go buying links directly on other people’s sites.
This discussion occurs at the 14:39 mark in the video below: