What to do about a dirty engine

Recently when I get out of my car, I can smell a smoky smell. My mother thought that maybe there are something wrong with the car and that, if left untreated, the car might explode. I have since spoken to an expert who told me that the oil leaks in my car. Because the oil leaks onto the engine, dirt sticks to the engine. Because the engine gets hot when it runs, it burns the dirt, producing that smoky smell. I asked him whether it was something to be concerned about and he said no. It was normal in old cars.