If you were to step foot on Mars without a spacesuit you'd last about 90 seconds before going unconscious - its atmosphere is 95% carbon dioxide. While lying there unconscious or dead, your blood will also boil due much lower pressure. Even though temperatures can reach 70F at the equator at noon, temperatures can be as low as -225F. The average temperature is -81F so, even if you could breathe, your lungs could freeze.
If you were protected in a spacesuit, you would feel incredibly light. Mars's gravity is about one-third that of Earth's, so if you weighed 100 pounds on Earth you would weigh just 38 pounds on Mars. All objects on Mars are two- thirds lighter than on Earth, so if you picked up a rock you'd be surprised at how light it is. If you then dropped that rocked, you'd see it falling to the ground much more slowly than on Earth