The 19th hole of any golf course is just another way of saying the clubhouse. This is where golfers can relax with food and drinks after playing golf.
Many golf courses have a clubhouse, which is a building at the start of the course where there are locker rooms and other amenities. Some clubhouses have bars, restaurants, and sometimes even pools. To become a member of a golf course, you usually gain access to all these things, giving you much more than just a place to golf.
Sometimes, although rarely, the 19th hole can also refer to a playoff between two players. A playoff occurs when two players are tied at the end of a competitive game, and a winner must be chosen. During a playoff, each golfer plays the 18th hole again, and whoever has the lowest score wins. This is referred to as the 19th hole.