@sbi gives you an upvote on every single one of your posts for life. You can buy a share for 1 Steem and in the process you will need to nominate one other Steemian. The steemian you nominate will also receive an upvote for life on everyone of their posts.

I have have about 10 shares and the upvote value I get is around 0.01 on every single post I make. The more shares you own the higher the upvote value you get.

So in short : you have to pay 1 Steem or get sponsored into the program.