When you buy a share you get a percentage of 5 upvotes a day. What your percentage is depends on the amount of shares in the program level.
The more shares the lower the percentage but the high the sp so you get more value the more shares are in the program.
There will be a window to remove your shares. All shares purchased with steem will include the proportion of grorth the account has seen. So all share holders own a part of the program.
When you sell your shares back they will be subject to a 10% fee.
I hope this helps. If you need further information please read the posts from @minnowbuilder