As long as enchanted creature is green, it gets +1/+1 and has indestructible. (Damage and effects that say "destroy" don't destroy it. If its toughness is 0 or less, it's still put into its owner's graveyard.)
As long as enchanted creature is white, it gets +1/+1 and has flying.
5/1/2008 If the enchanted creature is both of the listed colors, it will get both bonuses.
5/1/2008 If an effect would simultaneously destroy Shield of the Oversoul and a green creature it’s enchanting, only the Shield is destroyed.
7/1/2013 If a green creature enchanted by Shield of the Oversoul is dealt lethal damage, the creature isn’t destroyed, but the damage remains on the creature. If Shield of the Oversoul stops enchanting that creature later in the turn, the creature will lose indestructible and will be destroyed.