Input box is soemthing which will get a values for variables. This variable is then used in the chart's dimension or expression so basically it renders chats according to user input.
for eg, if we have a req llike u want to show only the values of orderid that is being given by a user u can create a calculated dimension like
if(Orderid=vInputBoxVariable,Orderid)
which will return only one order id
in expression u would write the other fields , ie info of the order id..