If you have squirrels that are trying to eat your bird food you put out for birds then you can use safflower seeds in the bird feeder which are not harmful to birds but the squirrels will not like the bitter taste of the safflower seeds and will learn to stay away.
You could also place safflower seeds in locations where the squirrels are and where you want to keep them away from and they might learn to stay away from those areas as well.
Motion activated strobe lights and motion activated sprinklers can keep the squirrels away from your yard as well.
Ultrasonic pest repellents can also keep squirrels away by putting out a high frequency sound that humans can't hear but squirrels can.