There are two ways to search in Windows 8:-
1) You can open up File Explorer and type your search in the search box (as highlighted below)
This will allow you to search for files stored on your computer
2) You can use the new search facility that is part of the Start Screen and Charms Bar - this will allow you to search through files, settings, programs and the web
This search works in two ways, either you can open the Charms Bar by moving your mouse pointer to the top or bottom right corner (or swiping in from the right of the screen if using a tablet), and clicking Search
Or you can just start typing your search on the Start Screen and the search pane will automatically open and start displaying results
You can then choose one of the results shown or click on the icon to see a full page view of the results
By default it searches Everywhere i.e files, settings, programs and the web - but if you wish to only search in a particular area you can click the downward arrow (as circled below) and choose