As you may be aware steemit (the website) uses on a unique type of database(blockchain). This database is maintained by a group of people (witnesses). Essentially, everytime you vote or post it is sent as a transaction to the database. The witnesses run software that checks to make sure your transaction is valid, and , if so, updates the database to reflect your transaction. Since this is a crucial task, witnesses with the most trust(votes) are given the most opportunities to update the database. Hope this helps.