A package is a queen and 3 pounds of bees (~12000). Put into a hive with foundation, they have to draw the comb before they can start storing food or the queen can start laying. They start dying immediately but there are no bees emerging to replace them for approximately 1 month. In that time, the population declines to less than ~5k and that limits the growth rate.
A package of bees is a living organism and needs to be treated as such. Keep cool and well ventilated. When you get home with your package, you can keep in the garage or basement until ready to hive. You may want to spray with a 1:1 sugar water mix about an hour before hiving.
Prepare your hive on the hive stand, remove covers and center five frames. Remove feeder can and suspended queen cage and cover exposed area of package. Inspect the queen and verify she is alive and active. I do not recommend the immediate release of the queen since the bees with her were strangers just a few days before. Depending upon the type of queen cage, you may have to remove a cork cap over a candy plug. The bees will have to chew through the candy plug to release the queen and by then should be ready to accept her as their queen. Suspend her between two frames so that the screen of her cage is exposed. Then shake bees down in package and dump into open area in center of hive body where frames have been removed. This process may have to be repeated a few times. Gently replace the frames into the hive body. The last one may not fit because of the space taken up by the queen cage. Just save it for later.
Leave this new hive for about a week. Use as little smoke as possible to inspect the hive after that week to minimize likelihood of the queen running. Gently remove the queen cage and verify that she has been released. If she has not been released for some reason but is still alive, you can release her directly between frames. If she has been released, dispose of the queen cage and take a quick look to see how the bees are progressing with comb drawing and whether you can spot eggs or larva in the comb. Finding either is sufficient to indicate that the queen is active and you can close up the hive. You should check again in another week and verify that the queen is properly fertilizing the eggs and female worker cappings are on the cells.