Configure Your SharePoint 2010's Site Search Settings

Step1: Application Management ->Manage Service Applications ->Search Service Applicaton

step2: Create Content Source

step3: Create Scope (use content source in creating scope)

step4: Create Managed Metadata

The search box is just a text box with the prompt Search This Site inside it. Immediately, you can create a custom search results page, define the set of scopes that appear in the drop-down list next to the search box, and determine whether the search drop-down list appears on the page. You set all these options for search in one place, but first you have prep work to do.

By default, the search box is configured to use your site’s search configuration settings. To configure your site’s search settings:

1. Choose Site Actions→Site Settings to browse to the Site Settings page for your site collection.
   The Site Settings page appears.
2. In the Site Collection Administration section, click the Search Settings link.
   The Search Settings page appears.
   
3. (Optional) On the Search Settings page, select the Enable Custom Scopes radio button if you want to use a search center.
   All your site’s searches will use SharePoint’s default search page. By choosing to use custom search drop-down lists, you can target your search results to a search center, which is essentially a custom search results page.
4. In the Site Search Dropdown Mode section, select the option that describes how you want all the search boxes in the site to behave.
   For example, if you want all the search boxes to show Scope drop-down lists, choose Show Scope Dropdowns from the list.
   Choose the option that you want to be the default for all search boxes in your site. You can configure individual search boxes to behave differently in the pages or page layouts where you use them.
5. Set the default search box target results page by entering the path to a custom search results page in the text box.
   By default, all search results for contextual searches, meaning searches that use SharePoint’s default search drop-down options, target SharePoint’s default search results page. With this option, you can choose to target another page, such as the page you entered in Step 3.

Reference:

http://www.dummies.com/how-to/content/configure-your-sharepoint-2010s-site-search-settin.html

http://social.technet.microsoft.com/Forums/sharepoint/en-US/3c6a1b69-de88-4257-a9b5-3ac19269adc7/limiting-advanced-search-to-the-current-site-only?forum=sharepointsearchlegacy

http://office.microsoft.com/en-us/sharepoint-server-help/define-scopes-for-searches-HA010241119.aspx