Patio furniture is typically not used in the late fall, winter and perhaps even early spring time frame depending on the climate of where you live. It is a good idea to clean that patio furniture and move it into a dry storage area like your garage for the winter. You can dramatically increase the life of your patio furniture if you keep it out of the winter weather of rain and snow.
It is typically best to use soap, water, and a soft brush to clean most patio furniture. If the furniture is wood, you should check with the manufacturer instructions to verify the right products to clean and maintain the furniture.
If you have storage space in the garage, it is best to move the furniture inside. If not, you can buy covers for your furniture to protect it from the rain.
Here is a great video from The Home Depot on various ways of cleaning your furniture.