The Davis Cup (men) and the Fed Cup (women) are played all year round. Whenever the tennis pros have a break from their super busy schedule, they gather up with their teammates and host or visit another country. That is as simple as it gets.
Tournament Format
There are 8 teams in each side of the draw (16 total). You DON'T want to know how they chose the 16...TRUST ME. It's like talking to a lawyer about a contract. Something about a round robin format and zones like world cup.
But after they get the teams...it is a normal drive to the end of the tournament. A committee figures out where the ties are played.
What the heck...TIE?
When two countries play each other, they call it a "tie." This messed me up for a very long time so it is really important to understand that.
In a tie there are 5 matches, 4 singles and 1 doubles over 3 days (friday - sunday). Friday, 2 singles matches are played. Saturday is for the doubles match. Sunday, the 2 more singles players play.
Every match is called a "RUBBER." So if USA wins 3 out of 5 Rubbers against Sweden, USA wins the Tie. If USA wins the first 3 right off the bat, the last two rubbers don't matter but they still are played. Those matches are known as "DEAD RUBBERS."
Why is Davis/Fed Cup Fun?
Well DAVIS/FED CUP is like a big party. Fans are allowed to make as much noise as they want in between points and are often VERY ROWDY. The players also really seem to enjoy playing for their respective countries. Sometimes the home team has crazy rules like unlimited shot tracker challenges.
Players that feed off atmosphere can become davis/fed cup heroes. Nobodies can make a great name for themselves. A lot of people really love to play for their countries and are really motivated.