This gives gymnasts the chance to get used to the equipment that they will be competing on, because gymnastics equipment can vary slightly depending on the manufacturer. (For example, the uneven bars could feel slightly bouncier than the ones a gymnast normally uses, or the floor could be harder.)
Since visual cues are an important part of gymnastics, this also gives the athletes a chance to try their skills in the competition venue, and get used to the surroundings and set up.
In podium training, gymnasts are given a set amount of time on each event, and can choose what they would like to do during that time. Some athletes complete entire routines, while others just do individual skills.
Podium training got its name when the decision was made to elevate the equipment onto a "podium" about three feet off the ground, to help the audience see better. When equipment is on a podium it also feels slightly different than if it was on a normal floor, even if the apparatus is exactly the same.
Go to the Glossary of Gym Terms