To smash something is to hit or throw it so hard that it breaks or is hurt. It's important to pay careful attention while you're driving so you don't smash into the car in front of you.
A running child can smash into her friend and knock her down, and an angry chef can smash a plate by throwing it on the floor. In the latter example, there's the additional meaning of "break into pieces." A smash can be a car accident, but it can also be a "great big success," like a TV series that starts slow but turns out to be a smash. This "hit" meaning dates from 1920s reviews of Broadway plays.