Voting bots are simply a way to promote content on the Steem platform. If you don't have a lot of followers and/or not a lot of Steem Power you can use the voting bots to promote your posts and get them seen by a lot more people. If the posts are good then you will gain more followers and more organic upvotes as a result.

The steem bot tracker website shows you all of the information you should need to promote your posts effectively using the voting bots.