That's how many hits-for-at-bats. For example, 2-for-3 is very good, it means in 3 at bats you got a hit twice. A hit here means you got on base and weren't walked. A pop fly isn't a hit, and a sacrifice bunt isn't a hit. 0-for-3 could mean that you struck out twice and hit a sacrifice fly, for example. A play in which the fielder can either get you or another base runner out (called a fielder's-choice) is not a hit, even if he decides to get the other runner out instead.
It refers to the time signatures on the cheers they performed.
Let's use the 2-4 scenario. It means 2 hits out of 4 total at bats. The player got 2 hits, and the other times he went up to the plate, he got out. (Remember, sacrifice plays and walks do not count as outs- in that case you would say 2-4 with a sac fly or 2-4 with a walk)
if they went 2 for 4 then they went up to bat 4 times but only hit and got on base 2 times
if they went 0 for 4 then they went up to bat 4 times but didnt get on base but that doesnt mean they didnt hit the ball they just got out
That's how many hits they had in a number of at-bats. (X hits in Y at-bats, or "X-for-Y"). That determines your batting average, both for the game and for the season. Those players went .667 and .500 respectively because you divide the number of hits by the number of at-bats.
It means that they got 2 hits when they were at bat 3 times.