General: How to get full information on a specific tournament? 

Event event = Snooker.API().getEvent(eventId);
where parameter eventId is ID of the tournament.

How to get full information on a specific match? 

Match match = Snooker.API().getMatch(eventId, roundId, matchNumber);
where parameter eventId is ID of the tournament which the match is played; roundId is ID of the round of the tournament; matchNumber is number of the match in the round.

How to get full information on a specific player? 

Player player = Snooker.API().getPlayer(int playerId);
where parameter playerId is ID of the player.

How to get information on all tournaments in the season? 

Events seasonEvents = Snooker.API().getSeasonEvents(season);
where parameter season is object of class Season that specify a season or Season.ALL for all available seasons.

How to get information on all matches of a specific tournament? 

Matches eventMatches = Snooker.API().getEventMatches(eventId);
where parameter eventId is ID of the tournament.

How to get information on the matches which take place in this moment? 

OngoingMatches matches = Snooker.API().getOngoingMatches();

 How to get information on all matches of a specific player in the season? 

Matches playerMatches = Snooker.API().getPlayerMatches(playerId, season);
where parameter playerId is ID of the player and season is object of class Season that specify a season or Season.ALL for all available seasons.

How to get information on all players in a specific tournament? 

Players eventPlayers = Snooker.API().getEventPlayers(eventId);
where parameter eventId is ID of the tournament.

How to get information on all players in a specific season? 

Players players = Snooker.API().getPlayers(season, category);
where parameter season is object of class Season that specify a season or Season.ALL for all available seasons and category is object of class PlayerCategory that specify a category of players (for example, PlayerCategory.PRO).

Additional: How to get information on the ratings/earnings of all players in the season? 

Rankings rankings = Snooker.API().getRankings(season, rankingType);
where parameter season is object of class Season that specify a season or Season.ALL for all available seasons and rankingType is object of class RankingType that specify a rating type (for example, RankingType.MoneyRankings).