A minus sign before a number greater than 100 (like -110) means the amount of money that you must bet to win $100. So, if the money line is WF Over 5 wins -110 and if a bettor bets $110 on WF to go over 5 wins, and WF wins 6 or more games, that bettor receives $210 (his $110 bet back plus $100 of winnings).
A plus sign before a number greater than 100 (like +120) means that amount of money that you win if you bet $100. So, if a bettor bets $100 on Duke to go under 5.5 wins and the line is Duke Under 5.5 +120, and Duke wins 5 or less games, that bettor receives $220 (his $100 bet back plus $120 of winnings).
You don't have to bet in $100 increments. The house will make the money line calculation regardless of how small (you could bet $11 to win 10) or how large (you could bet $1100 to $1000) the bet is.