To use the MailChimp for WordPress plugin, you will first need to connect the plugin with your MailChimp account.
Get your MailChimp API key
Log into your MailChimp account and then follow this link to get your MailChimp API key (or go to Account > Extras > API Keys).
Configure the plugin
To let the plugin know which API key to use, go to MailChimp for WP > MailChimp in your WordPress admin area to fill out your API key.
Alternatively, you can set the
MC4WP_API_KEY PHP constant instead.
Using the settings form
Using the PHP constant
define('MC4WP_API_KEY', 'your-api-key-here' );