You mean when they have multiple boards of community cards in one hand?
That only happens in cash games, when the players in the hand are all-in and they agree to "run it" multiple times. The pot gets divided by the number of runs, the cards (or remaining cards, if it's post flop) are dealt and the portion of the pot goes to the winner of each run.
Player 1: AdAs
Player 2: AhKh
Flop: Qh Js 3h
Players get all their money in and agree to "run it twice"
First run turn/river: 2d 7c
Second run turn/river: Tc 9d
The players would get half the pot each. Player 1 wins the first with a pair of aces. Player 2 wins the second with a straight.
I don't remember to have seen second board on the micros , there's no reason , but I wouldn't do it , I mean , if sb asks for a second chance and you agree , on another hand where he will have the best hand will he agree to run twice and how would you know ? I wonder ... I had this option diabled from the beginning .