New to the platform questions

When I see a game that might say ( 19 Current Players   (6 Open Slots)      I assume that there are not 25 players in the single session. What is this refering to and how are the slots filled. Is it a first come first serve type of thing?   Secondly, If I see a game that say starts the next day, and I see a count of 3 current players (2 slots open). But then I go to the sot request page and see 20 applications. What does this mean... has the DM not selected to fill the slots or is the information just not updated...?   Thanks for any feedback you all can provide.

All games on Roll20 are run by humans. That means that some people run games with a very large pool of players where only some show up for some games. Some may have a date set for their game, but not filled their player count, or forgotten about the game altogether. Some people take this stuff more seriously than others. The one thing you can be certain of is that if you go to a game's page and look at the player count, that's an accurate number of the number of players currently part of the game. Everything beyond that is up the the DM(s) of that particular game. There may be many players that joined ages ago and never log in again, or maybe they really do play with 25 people at a time.

Some games/campaigns might just act as a central hub for a collection of players/DMs who may or may not organize all games in that specific game/campaign, and might have other games that are the "real" games, while jsut using the larger game's Forum to communicate between community members on when/what games to join and where to play. For example, I'm part of a Star Wars D6 "game" with +100 "players", and it's just for organizing finding folks to play with, not an actual active game itself.

Thanks very much for the feedback.