A sports betting model is a system that can identify unbiased picks to determine the probability for all outcomes in a certain game.
At a functional level, the goal of a model is to highlight profitable betting opportunities by being more accurate than a bookmaker.
Needless to say, building a successful sports betting model is not easy. If it was easy, everyone would have their own model that could beat sportsbooks and sports betting wouldn't exist because sportsbooks would not make money.
Bookmakers usually have their own model in order to create betting lines, so the goal for a personal betting model would be to create a better, more efficient one.
There are a number of factors that go into building a sports betting model.
Clearly, one does not set out to create a sports betting model without an initial goal or basic knowledge of mathematical concepts. There's a reason betting models are only common for sportsbooks or full-time bettors. They take time to create and then you have to tweak them if something is off. It's an ongoing process that changes by the season.
However, if you find a fault in the betting odds and have the capabilities, a betting model is a good way to turn a net positive.