If you see bees flying in and out of a hole in your soffit -- which refers to the underside of arches, ceilings and exterior overhangs on a roof -- you may have a big bee problem on your hands, and you should deal with it as soon as possible. Bees love to set up their home under soffits, as the space underneath a soffit is usually just the right size for a nest. Generally, you should call a professional pest service to deal with this problem; but if you insist on doing it yourself, you can take a few steps to get rid of the bees for good.
Put on a beekeeper suit -- the all-white suit and helmet you see beekeepers wear to avoid being stung -- before attempting to get the bees from the soffit, and clear everyone from the general vicinity.
Pull back the soffit to expose the interior. Do this during the late evening or early morning hours, as bees are less active in cooler weather. Use a bee smoker before attempting to remove the hive, as the smoke helps calm angry bees. Apply insecticide to kill as many bees as possible.
Remove the nest, and place it in a garbage bag. Discard it in an area far enough from your home that any remaining bees won't bother anyone. Smash up the hive by stomping on it or burn it so it can't be used again.
Replace the soffit. Use the caulking gun to seal any cracks or crevices to prevent bees from building a hive again.