From the faq:
Stackers reward each other for their contributions by zapping them with sats. To start earning sats, you can share interesting links, discussion prompts, or comments with the community. Beyond the direct payments from other stackers, Stacker News also uses the revenue it generates from its job board, boost fees, post fees, and stacker donations to reward stackers that contributed to the site with even more sats. Every day, Stacker News rewards either creators or zappers with a daily reward. These rewards go to stackers who either created or zapped one or more of the top 33% of posts and comments from the previous day. The rewards scale with the ranking of the content as determined by other stackers. Finally, Stacker News also rewards stackers with sats for referring new stackers to the platform. To read more about the Stacker News referral program, click here.