How do upvote/downvote bots works?

So if you post in introduceyourself tag you will see instantly that some 4-5 bots will upvote your post and will comment on that.New user who have no idea about them try to reply them and unknowingly try to have a discussion with bots which lower the overall user experience of the platform. So I want to know how these works and what good they do to their author ?