Before I can begin answering it, we must first start by understanding what a space suit can provide for you and other astronauts. A space suit provides pressurized air so that your bodily fluids do not boil. They act like tires or inflated balloons made of rubber fibers to keep air pressurized inside the suit. They also provide oxygen for you to breathe so that you do not suffocate. They remove the carbon dioxide that you breathe out of your lungs. Large amounts of carbon dioxide are very dangerous and can be deadly. Because of the extreme temperatures of space, space suits are insulated with heavy layers of fabric to keep the temperature inside constant and comfortable. The fabric also protects from tiny meteorites that collide into the suit. To protect from harmful radiation especially from the sun, space suits have reflective coatings of Mylar that are built into the suits. Space suits also come with durable helmets that reflect sunlight and reduce glare like sunglasses. The joints of space suits such as the knees or elbows are tapered to give you freedom to move when you are wearing them. They also come with radio transmitters and receivers so that you can communicate with other astronauts or controllers. These are the many wonderful things that space suits provide for astronauts. But if you did not have one on, the list below describes what would happen. I hope you remember to put one on the next time you go into space!

You would become unconscious within 15 seconds because there is no oxygen. Your blood and body fluids would boil and then freeze because there is little or no air pressure. Your tissues (skin, heart, and other internal organs) would expand because of the boiling fluids. You would face extreme changes in temperature:
sunlight: 248 degrees Fahrenheit / 120 degrees Celsius
shade: -148 F / -100 C

You would also be exposed to various types of radiation, such as cosmic rays, and charged particles emitted from the sun (solar wind). You could be hit by small particles of dust or rock that move at high speeds (micrometeoroids) or orbiting debris from satellites or spacecraft.