In Magento 2 you cannot perform the reindex from the back-office. To make a reindex you need use PuTTY or another terminal application to run the CLI commands, e.g. command for reindex:
php bin/magento indexer:reindex
With FREE Magento 2 Command Line (CLI) Extension by Magefan you can run CLI commands directly from Magento 2 admin panel.
Once you install Magefan CLI extension a new menu item "System > Command Line" will be added to the admin menu.