You put oil in your lawn mower and now its smoking?

More than likely you filled it up beyond the recommended capacity. Check the level on the dipstick and if it shows more than the recommended capacity, drain some oil out of the engine. If it is a push mower, you can turn the mower on its side just enough to drain a small amount at a time. Or, you can access the oil drain plug from underneath the engine. Most riding mowers will have the drain plug on the side of the engine. The engine may continue to smoke until all the oil in the combustion chamber is burned off.