Menu->Search simply pops up the default search widget.
Tapping in the box brings up the virtual keyboard to enter a search term or you can open the physical keyboard. Here is a search for 'backflip':
Tapping on one of the suggestions will open the Yahoo search page in the browser with results for that suggestions:
Using Menu->Search is the same as using the search widget.
You can also bring up the search widget by pressing the maginfying glass key on the keyboard.