How do you determine the start of the next inning in baseball?

Answer 1

when you retire the side and get three outs then it will go to either the next inning or next half inning

Answer 2

With a pitcher pitching to a batter who is trying to hit the ball and it starts with either him getting out, getting a hit, or getting walked.

Answer 3

The first inning starts when the umpire calls "Play Ball." All other innings start immediately after the third out of the preceding inning.

Answer 4

After 3 outs, this is for the rest of the innings as well.