Magento 2 provide us the ability to take more control of the customer account creation process, setting an special configuration located under admin under Stores → Configuration → Customers → Customer Configuration → Create New Account Options named Require Emails Confirmation (Yes/No)
If you set this setting to Yes, a customer will not be able to log in without account confirmation. He needs to click the activation link in account confirmation email.
Unfortunately, there is no way to confirm the user account from Magento 2 admin area, but if you are a developer, you can confirm it through a simple database query, removing the hash value on the confirmation field of the customer_entity table, as follows:
UPDATE customer_entity SET confirmation = NULL WHERE firstname.lastname@example.org';
Note: The confirmation email is on vendor/magento/module-customer/etc/email_templates.xml file.