How to get backlinks

Hello there, I was wondering how do guys get backlinks to make? Are there any sources, sites, technique, where we can get backlinks.

Currently I use Mangools link miner tool (paid) to extract backlinks. I extracted all the backlink from my competitor sites and other niche related to my blog.

Don't know if I can extract links from other sites of different niche? So don't know what to do.

would love to know what you guys do to extract new backlinks for link building.