Opera 10's Preferences dialog should now be displayed, overlaying your browser window. First, click on the General tab if it is not already selected. Next, locate the section labeled Home page.
In the example above, the home page is set to http://portal.opera.com. To change your home page, simply replace this URL with the Web address of your choice.
If you would like to set the current page that you are viewing within Opera as your home page, click on the button labeled Use Current.