What is this new bounty and vote up buttons I see beside the answers posted for the questions?
You can vote up good answers and vote down bad answers. A vote up earns the person who gave that answer points. Answers with many down votes will be hidden.
When you ask a question, you can select a Best Answers and the person that gave this answer will receive extra points (the bounty).
Make Use Of members get points for answering questions. Some people were posting garbage answers as a way of gathering points without making a useful contribution. That devalues the web site.
Some web sites I've used in the past allow that, Make Use Of did until recently and we were seeing some abuse of the system.
If nothing had been done to address the problem the result would be that you might have to wade through hundreds of garbage answers to a question before you'd find one that's useful.
If you post a question and get a good answer you are encouraged to mark it as "solved", that helps but many never bothered to mark it as solved.
A voting system allows the rest of us to register our opinion about an answer. That can be used 2 ways (not sure how it will be used here). Answers getting a lot of up-votes may be listed higher up the results than others and whoever posted an answer may be awarded some points related to the number of up-votes.
It seems to me that the guys at Make Use Of are keen to provide a quality Q&A service and are actively developing it so I expect more changes as they refine the rewards system.