Like many furry animals, cats' fur gets thicker in the winter to help protect them from the cold weather. When it gets warmer, they no longer need this fur, so they shed it. This works well in nature, and definitely helps your cat deal with the change in temperature, however, this is brutal to a clean home which now has loose cat fur everywhere!
There are ways to tame this fur so that it does not get all over your house. The best thing that you can do is to brush your cat regularly. Normally, a long-hair cat should be brushed daily, and a short hair cat should be brushed three times a week. Once you notice them shedding for the summer, you may wish to up this frequency.
I have found that the best cat brushes are the ones with metal tines. These get in deep to get all the loose hair in every layer of the cat's fur. The tines are generally close enough together that they capture the fur efficiently as well. These are also great because they give your cat a great massage, often the cats will begin to 'ask' for brushings! My favorite is the Furminator brush. A great advantage to using a metal brush is that it efficiently distributes the natural oils in your cats skin. This makes their coat look silky and feel smooth. You may have a preference for a different brush though. I have heard that the rubber molded ones work well too.
Another issue that your cat may have this times of year, in addition to losing a lot of fur, is that their claws will begin to molt too. This does not cause as big a problem as the fur, but you may find what looks like whole nails on the floor. These are just the molted bits, think of it as when a snake sheds its snake-skin.
After you have your cat's shedding under control, you will want to work on your home. You need to get rid of all that cat fur that has accumulated everywhere! For most fabrics, I would recommend a lint roller. Lint roll the fabrics before they go into the wash, or else you may clog up your washing machine. For the floor and other hard surface areas, try a microfiber cloth, or a dry Swiffer pad. These are both great at picking up dust and animal fur.