From where does SP get for new users (the SP given in parentheses) and when will it disappear?
It's called delegated Steem Power and it will go away after 1 month or stay until they take it back if somebody give it to you.
There is also a small amount stored in the new account and is permanent. That had to be paid for by whichever account created it (usually 'steem' which is owned by Steemit)