Dennis, if you have sustained hail damage the shingles will show areas where the granules will have become dislodged from the shingle. You will be able to see the asphalt of the core of the shingle. While this does not usually present an immediate danger, if left alone the asphalt will decay from UV exposure and will become a leak problem. You will see areas that have become dented, granule loss or spots where the shingles may have fractured.
If you get up on your roof, DO NOT go up there alone. have someone on the ground incase you get in trouble. Wear soft sole shoes. Take a piece of foam cushion if the roof is slightly steep to help hold you on. make sure the ladder is well secured to the gutter or fascia board and by all means DO NOT take any chances. If you feel the least bit uncertain about being on a roof call a local, established roofing contractor to come and give you a roof inspection.