Access Modules Page
Go to the modules page. Administer >> Site building >> Modules
Find the Search Module
Scroll down and find the "Core - optional" section.
Enable the Search module.
As the image says, save the configuration.
Check our Search
Beautiful!
Advanced Search Configuration
Administer >> Site configuration >> Search Settings
In Search Settings you will be able to re-index your site, change indexing settings, and specify the maximum number of items to index per cron run.
You will also be able to specify which properties (i.e. Keyword relevance, Recently posted, Number of comments) about the content are more important in terms of page ranking.
Save when finished.
Permissions
To modify the permissions for the Search module, go to Administer >> User management >> Permissions.
Then scroll down to the Search Module.
By default, anonymous users cannot perform searches. However you can modify it here by selecting the desired options.
Save when finished.