@steembasicincome is basically an upvote service. Each share you get of SBI increases the strength of the upvote you receive from SBI. Here is more information on it:
https://steemit.com/basicincome/@steembasicincome/steem-basic-income-a-complete-overview
Should I only register to receive the votes? ... that is, transfer the steem.
You do not need to do anything or transfer anything. I sent in 1 steem for 1 share of steembasicincome in your name. It takes about a week for them to update everything and get your shares on the list before you should seeing any vote from them.