Short answers, pulled from the story.
Three points for a win means a team receives 3 points for winning a match, 0 points for losing, and 1 point each if the match is drawn. It replaced an older format used by many leagues that gave 2 points for a win and 1 point for a draw.
The system was introduced in England in 1981 after Jimmy Hill proposed it for what was then called The Football League. It did not spread widely elsewhere until it was used at the 1994 World Cup finals.
FIFA formally adopted three points for a win in 1995 partly because it is thought to encourage more attacking play, since a possible late winning goal is worth more than the single point risked by conceding one. It is also thought to discourage teams from settling for a draw to advance or avoid relegation.
In Group D of the 1998 World Cup, Nigeria finished ahead of Paraguay under three points for a win despite Paraguay's better goal difference, a result that would have been reversed under the older two-point system. Similar flips occurred in Group D of the 2015 Women's World Cup and Group F of the 2010 World Cup.
Yes. Versions of the three points for a win system have been adopted in ice hockey, field hockey, volleyball, water polo, bandy, floorball, camogie, and Ladies' Gaelic football since the 1990s. Many of these sports, especially ice hockey, use modified point values for overtime and shootout results.
A three-point proposal for the NHL, worth 3 points for a regulation win, 2 for an overtime win, and 1 for a tie, was proposed in 2004 but paused by the 2004-05 lockout and rejected by team owners in February 2007. The NHL instead uses 2 points for any win and 1 point for an overtime or shootout loss.