The SP is an average of prices taken from across the betting industry. Meanwhile, 'BSP' stands for 'Betfair Start Price' and this simply refers to the price in which a horse, team or outcome is priced up at on the Betfair Exchange at the exact time that the event starts.
An acca is a group of individual bets brought together in one mega wager. Each leg of your acca, or accumulator, must win in order for you to win the overall bet and get a payout.