I am relatively new to Steemit and had the same questions but if you read the FAQ you will learn a lot about the platform. As far as voting is concerned you can lose voting power if you vote too much. Every vote on a post uses about 2% of your voting power and dropping below 80% your votes don'reward as much of your SP. this section of the FAQ explains it better but i went down to 40% just upvoting everything and the rewards being shown dropped because of it. https://steemit.com/faq.html#What_is_my_voting_power