How do you Calculate ROI and finding good bets

[Diracdelta]

Hi
Just getting started with sports betting. Have found a few sites that give recommendations on bets. They use a number called ROI, that is about 105-110%, when they describe how well their "betting fund" has grown. I would like to know how you calculate this number. And what this number actually means. Also if you could recommend some site that gives good betting picks for free, or for a acceptable fee.
/Pete