If you are new to the steemit community, first a warm welcome and even if you are not new you may have a few questions about what the dollar values next to the posts mean.
When you make a post as it is voted upon according to other users it gains value depending on who is voting on the content. People who have invested lots of money or have created great content or both have the most potential to increase the dollar amount of a post.
When you see a post with $100 next to it what this means is that at the end of 24 hours the following happens
As per steems whitepaper "When a post receives a payout it takes the form of 50% SMD and 50% SP. The Steem Power give the user increased voting and transaction power while the SMD gives the user an immediate benefit in a stable currency. As we’ve already discussed at length, both SP and SMD are designed to encourage long-term holding rather than short-term selling."
So for a post that has $100 next to it you will earn 50 Steem Dollars (SMD) (Which can be converted to steem and then cashed out or invested in steem power giving you the chance to increase the impact of your vote). The other 50 you receive is in the form of Steem Power already (This determines how much weight you have when voting or receiving payouts).
To the best of my knowledge in replies to an original post (also known as a parent post) the original poster gets 50% of the payout of the upvoted responses to the post. So creating content that has people commenting with interesting responses can benefit both the person who makes the content and the person who responds.
I can say honestly this is the most exciting use of blockchain technology that I can think of so far.
Feel free to ask any questions you may have and I will do my best to answer. Hope everyone is having a great day!