Each partnership adds its two bids and has to take at least that many tricks. Make it and you score ten for every trick you bid, plus one for each extra trick. Those extras are bags. Bid four, take five, and the hand is worth forty-one. Fall short and you lose ten for every trick you bid.
A nil bid is a promise to take no tricks: a hundred points if it holds, minus a hundred if it fails, scored on its own while the partner's bid is scored on the partner's tricks. Bags carry from hand to hand, and every ten your side collects costs a hundred, so keep a running bag count in its own column. The first side to five hundred wins.
At other tables
Many tables also allow blind nil, bid before looking at your cards: plus or minus two hundred. Others play to three hundred or a thousand, value nil at fifty, or drop the bag penalty. Source: pagat.com
This is how Cards Royale scores Spades. The full rules are on the how to play Spades page.