Per the rules of the expansion, each manager will have at least one challenge per game. If a manager uses and wins a challenge, he would be awarded another one. Additionally, umpires (crew chiefs specifically) will have the option to call for reviews from the seventh inning on.
The calls in question will all be reviewed at a command center in New York (not at the ballpark). Stadiums will also be permitted to show all replays on the scoreboard at the game.
Plays that can be challenged are home runs, ground-rule doubles, fan interference, boundary calls, force plays (with the exception of the neighborhood play at second base), tags, traps (outfield only), hit by pitch, whether a runner scores before the third out is recorded, passing another baserunner and correct counts.
For the full replay rules, click here.