Yes. I am enrolled already. The only way to get a share is to be sponsored by someone else. Basically they pay one STEEM to @steembasicincome and mentions the name of someone else. Then they and that mentioned person get one share (so I did benefit from sponsoring you). Thereafter they both get upvotes on all of their posts forever.

Yes you could sponsor me by sending one STEEM the same way with my name as benefactor. Then I would have two shares and you would have two. We would not then get two upvotes but one upvote for each post that was double previous (I dont know if it scales linearly like that exactly but it is close I believe).

I like to use it to sponsor those with good content or people with low SP and good content. It is important to give it to active posters for full benefit. You get nothing if you do not post. That’s why I said no pressure :/)

Search for SBI contest. There are many every week. Many that recur regularly. Some are random and some require some action or task.

You can also get shares by delegating steem power to SBI but i wouldn’t do that until you are more established and had more and growing SP.