I got the answer you are looking for @knircky.
I sign up and the answer from their support team.
What is sorting?
Sorting, or picking the best of two responses presented to you at one time, is the main action by which the best responses get curated to the top for more users to see. Additionally, sorting determines how the bounty is distributed across responses.
How do I sort replies for ETH?
Select the 'Sortable' filter on the main feed.
Click to view the post and scroll down below the post until you see the "SORT FOR ETH" button and click it.
You will be presented with pair sets of 2 replies each. Simply click the arrow that indicates which reply you think is "better."
20% of every bounty gets distributed amongst every user that sorts any replies based on the proportion of total number of individual sorts they've made in relation to the total number of sorts overall.
I hope it's helpful