If the spread is set at +7, the underdog must either win the game outright or lose by fewer than seven points in order to cover. For the favorite to cover, they must win by more than seven points.
Betting odds are the ratio between the amount staked by the bookies and the bettor, so 7/1 means the bookies stake seven times the amount the bettor has wagered. If the bettor wins; their predicted outcome materialises; they will take seven times their bet from the bookie (in this case).
One bettor won more than a half-million dollars by hitting an insane parlay during Championship Sunday in the NFL. The lucky winner turned their $20 site credit on FanDuel into $579,000 by correctly guessing the winners and exact score of both conference championship games. There's 55 555. There's just 55 555.
A good medium is 3% per play. For example, if you're starting with a bankroll of $100, you should risk $3 on every bet. If you're starting with $1000, you should risk $30 on every bet. Your unit size would be $3 or $30, respectively.