With the help of visualforce pages, we can override standard buttons. First, we can create visualforce page and overriding the standard new button with created visualforce page.
After the creation of vf page, the next step how to override the standard opportunity new button.
Go to setup -> opportunity -> Buttons,links, and actions -> Click on Edit button.
select override with the visualforce option and select “name of the Vf page” you created above and save your changes.