Hello,
You may have turned the gas tank valve on too fast. Turn it back off, disconnect it and reconnect it. Then very slowly turn the valve back on. Light one burner at a time and turn to low before lighting the next. If you are hearing and smelling gas with the tank on but all grill knobs off, don't use the grill. You may have a leaking grill valve, regulator or hose. If you are only smelling gas with the knobs on, it's possible you have a clogged burner or orifice from bug nests, spiderwebs, etc and need to clean it out first. Hope this helps. Douglas