Welcome to steemit. The dollar amounts are your share of the daily STEEM value created by the system (every day a certain amount of steem is generated and released to content creators). The amount that you get is decided by the votes that you get on your post. Not just the number of votes, but also the weight of those votes. People that hold more steem in the form of "Steem Power" have a higher vote weight and thus attribute you a greater share of the days currency. People with less steem power attribute you less. There are some very large holders (like the founders dan and ned) that have a vote that is worth whole dollars because they have larger stakes in steem (they are the ceo's after all).