Something volitional is done on purpose, like deciding to walk to the library to return your overdue books.
When someone does something of their own volition, it means they meant to do it. Likewise, volitional acts are also things done deliberately. Most of our actions are volitional — you likely meant to go to the store, watch your favorite TV show, or hang out with your friends. If someone forces you to do something, it is not a volitional act. The root is the Latin word for "I wish," volo.