User409696431 posted
That is a very general question. What don't you know how to do? Store the information in a database? Query a database based on the value in the field containing the voucher number? Get that number from an input field in the page?
Redirect to another page? How will that page be selected, if it is not the same page for everyone? What kind of site are you creating: Web Forms? MVC (full framework)? Core?
Normally, this forum is for you to share the code you have tried, in order to get help if it doesn't work. The "Learn" tab at the top of these forums is where you can start from the basics.