I recommend you to install it with composer since it will be easier to update it. If you have SSH access (command line access) just use the command
composer require mailchimp/mc-magento2
in your Magento root directory.
And next of course do a
php bin/magento setup:upgrade
php bin/magento cache:clean
php bin/magento setup:static-content:deploy
Now if you ever do the command
composer update it will automatically update your MailChimp also.
Your website has a newsletter subscription standard. I believe that MailChimp will use that to sync with their API. So its bound as default. You do not have to bind it to anything specially as long as your customers appear in Marketing->Communications->Newsletter Subscribers