The Twingine site contains a blank search form into which you can type any search query. When you click Search, the site brings up the results pages for that query from both Yahoo! and Google, side by side. Clicking Next or Previous in the top frame at Twingine takes you to the next or previous page in the search results at both sites.
When you want to open a link, you would do well to open the link in a new tab. Otherwise, the new page will open within the frame in which you clicked the link.
If you like to use Bing instead of Yahoo, click the Bing! link in the top frame.