In order to enable search feature in your site, ie, users can search for specific keywords in your site content, you have to run a cron job.

Cron is a daemon that executes commands at specified intervals. These commands are called "cron jobs." Cron is available on Unix, Linux and Mac servers. Windows servers use a Scheduled Task to execute commands.

Every Drupal install requires regular actions to handle maintenance tasks such as cleaning up log files and checking for updates.

For a modest personal site, you might set up this cron job to run once a day. For a more active site you might want to run that job more often—perhaps every few hours or every hour. This regular visit will tell Drupal to perform its periodic tasks, and this will help keep your system running smoothly.

Run cron to enable search: Go to Admin > Reports > Status report.

Master Drupal in 7 hours - Advanced Customization - Search - Run cron_01
 
Master Drupal in 7 hours - Advanced Customization - Search - Run cron_02