Odds with a plus sign are underdog bets. Plus odds tell you how much profit you will get on a $100 bet. A $100 bet with +200 odds nets you $200 profit plus your original $100 bet. If you bet $20, you would profit $40. For the rare even money odds, those can be listed as -100, +100 or EV.
The great thing about the DraftKings bet $5, get $200 bonus is that you get multiple rewards when you claim it. Not only do you earn $200 in bonus bets when you wager $5 on your first bet, but you can also claim No-Sweat Bet Tokens when you wager on a same-game parlay every single day.