To send emails from the application, you must configure the mail driver in app's configuration panel.
Go to Configuration Page and click on the Mail to go to Mail Configuration
The log driver doesn't send any email. It only logs the email in storage/logs/laravel.log file
To use the Mailgun driver, you must have valid & active mailgun account. You need to add your domain in your mailgun account & activate it. Once activated, you can use your domain, secret key & mailgun end point to send emails.
To use the SMTP driver, you must have a valid SMTP carrier. If you use Gmail SMTP, please make sure you have disabled less secure app option in your Gmail account.