If a score is 6-1 in 5th inning in MLB and they quote Team A RL 0 at -110 that means the score is 0-0 when you place your bet
Most books offer like -5 or +5 runs or a ML of like -700 on the team that is winning when the score is 6-1 which in my opinion is simpler to understand
Live betting is one of the few times the oddsmakers don't have hours and hours or days, even weeks to produce the lines. I have won some of my bigger bets via live betting. JJ makes a good point. The rules are different and make sure you are watching the game. At the very least get advice from someone at/watching the game.