Shining visible radiation from a torch beam onto a hand lights the hand up because the hand has been exposed to light.
Irradiation from radioactive decay can damage living cells. This can be put to good use as well as being a hazard.
Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a radioactive source - typically cobalt-60. The gamma rays emitted by the cobalt will destroy any bacteria on the fruit but will not change the fruit in any significant way. The process of irradiation does not cause the irradiated object to become radioactive.