You can choose to decline payment as an option when you are creating your posts. It is in a drop down menu at the bottom right hand side when you are in the editor.

Post are paid from coins created by the blockchain from what is called a 'reward pool'. The reward pool is paid out according the the voting power of the accounts that vote for your post.

Voting power is derived from the amount of Steem an account has that has been locked up in the form of Steem Power. Basically, the more Steem an account chooses to lock up as Steem Power, the more influence the account has on the distribution of rewards.

You can choose to ignore it all if you wish. You don't owe anyone any money. You are actually making money should you choose to take your Steem tokens to an exchange and sell them.