Individual (Singles and Doubles) Competitions
Each year there are 4-5 "World Championship Series" tournaments held on each of the official ITSF tables (which are currently Tornado, Bonzini, Roberto Sport, Garlando, TecBall). These determine the best player(s) in the world on those specific tables - the best Bonzini players in the world are determined at the Bonzini World Championship Series tournament, the best Garlando table players are determined at the Garlando World Championship series tournament, and so on, with the best Tornado players in the world being determined at the Tornado World Championship series.
Then, at the end of the year, the winners of all those World Championship "series" tournaments, along with other players who "qualified" through various methods meet at the ITSF "World Championships" (note the difference between it's name and the others that are called "World Championship SERIES") to play in an event incorporating all 5 ITSF official tables to determine the best "FOOSBALL" player(s) in the world (not just the best players on Tornado in the world, or the best Bonzini players in the world, etc).
The above all refers to individual players competing for themselves, not their countries. See the Individual Competitions page for more information on individual (singles/doubles) events.
Team (Country against Country) Competitions
However, also held at each of the annual World Championship "Series" tournaments are "ITSF National Team" events, where each country competes on that tournament's table only (i.e., at the Tornado WCS event it will only be played only on Tornado tables, at the Bonzini World Championship Series tournament it is only played on Bonzini tables, and so on for the other table tournaments) to see who is the best National Team/country on that table type for that year. Each country's team consists of several players, who play the team members from other countries in various configurations in doubles and singles to determine a winner.
Then, at the end of the year, similar to the individual competitions concept described above, the country against country "multi-table" TEAM tournament (called the "World Cup of Table Soccer," first held in 2006 in Germany) is held in conjunction with the ITSF (individual players) World Championships. This pits teams of several players from each country against other countries, playing on all five ITSF official tables, to determine the overall best "Foosball" playing country in the world.
See the Team Competitions page for more information on National Team/World Cup events.