ASP.Net App. and Back Button Browser.

Question

Hello to All, I have one scenarion and I need to take one action in order to delegate the project development. I have one Web App. one webform the user will provide some charge information to one account, how can I Prevent once the user has been press the submit button and the charge has been posted and by error the user press the back button and the last page appear, what and will happen? The use will post again the charge? The page will autopostback? Please help me... Regards