SharePoint sites come with a search field built into each page of the site by default.
For search results to return anything back, the Farm administrator has to configure the Search Service with content sources and the content has to be crawled and indexed by the service. Typically, the crawling process is scheduled to run automatically by the Farm administrator. When new content is added to a site, it will not show in search results until the crawl process has run and updated the Search Service's databases and indexes.
The following walk-through will show you how to add new content to your root team site and the child site Sub Site A and then perform a search for the newly added content. If you do not have a child site named Sub Site A any child site will do.
You can only perform these steps if you have access to the Central Administration site of your farm.
If the content source's Status is not Idle, click the Refresh link as described in the next step. Note that in a production site crawls would be scheduled to run periodically and you would not have to manually start them.