The reaping balls held slips of paper with the names of children from age 12 to age 18, two of which from each district for a regular Hunger Games. There were two reaping balls, one for boys and one for the girls. During the reaping, the reaping balls were placed on a stage in front of the Justice Building for the district escort to choose a name from each.
The Ballad of Songbirds and Snakes
For the 10th Hunger Games, the names of the tributes were placed in two burlap sacks, placed between either side of the mayor, rather than the escort, as there were none at the time. During the reaping ceremony in District 12, Mayor Lipp drew the slips for Lucy Gray Baird and Jessup Diggs. It was later revealed, however, that his daughter Mayfair Lipp had convinced him to pull out Lucy Gray's name.
The Hunger Games
During the District 12 reaping for the 74th Hunger Games, Effie Trinket was the escort who picked the tributes. She chose Primrose Everdeen from the girls' ball. However, her sister Katniss Everdeen volunteered for her. Effie then chose Peeta Mellark from the boys' ball.
In District 12, being that there were only three victors alive: Katniss, Peeta, and Haymitch Abernathy, Effie had to claw around the females' ball for a few minutes, despite there being only a single slip of paper with Katniss' name in it. She then chose Haymitch out of the males' ball, but Peeta immediately volunteered in his place.