sessionStorage gets erased every time you close the application. Other than that there is no difference.
Here is the usage example:
var keyName = window.sessionStorage.key(0); //Get key name
window.sessionStorage.setItem("key", "value"); //Set item
var value = window.sessionStorage.getItem("key");// Get item
window.sessionStorage.removeItem("key"); //Remove Item
window.sessionStorage.clear();//Clear storage