You can buy whole kernel corn at a feed store or at a farm that grows corn, you can buy cracked corn anywhere you buy bird feed. If you set up a feeder especially for squirrels you can set it right on the ground, that makes it easy to keep filled and the squirrels might stay away from your feeders that you have set up for birds. Nest boxes for squirrels are pretty easy to make and the squirrels really like them better than the nests that they make themselves. Nest boxes are fun to put up because you have a much better chance at watching baby squirrels when they come out to play. The main natural enemy to squirrels are weasels , foxes , coyotes, bobcats, birds of prey and owls.
Gray squirrels strip bark because they like to eat the soft sap part of a tree.
There is also what to do with a found baby squirrel there. I took that picture above right through my window. We have a bird feeder in that tree .