WPChimp can be installed like any other third-party WordPress plugin.
You can use one of two approaches:
File Upload Installation
If your server allows it, the easiest way to install this plugin is to upload the zip file that you have downloaded.
Go to your site’s administration panel, browse to the Plugins / Add New / Upload section, click on the “Choose File” button, select the zip file from your computer and click the “Install Now” button.
After the installation is complete, click on the “Activate Plugin” link to activate your newly installed plugin.
Manual Installation
On some servers, the upload method will not work. In this case you need to install the plugin manually.
You will need a way to upload files to your WordPress installation directory. Usually, you can do this by using FTP or SFTP.
To install the plugin, extract the downloaded zip file and copy the resulting directory to [wordpress install directory]/wp-content/plugins on your server.
After you copy the files, go to your site’s administration panel and browse to the Plugins / Installed Plugins section. In this section find the WPChimp plugin and click on the “Activate” link.
Connect WPChimp to MailChimp
Once WPChimp is installed and activated, you need to connect it to MailChimp.
Before you start, you will need to find your MailChimp API Key.
To get your API Key you can follow the instructions below or read this MailChimp knowledge base article: https://kb.mailchimp.com/article/where-can-i-find-my-api-key
To get your API Key, login to your MailChimp account and browse to Account Settings / Extras / API keys.
On this page, find the “Your API keys” section, click on the “Create A Key” button and a new key should be added to the list. Copy the code from the API Key column (this is what you need for WPChimp).
After you have the API Key, go to your site’s administration panel and browse to WPChimp / Settings.
In this section, fill in the “MailChimp API Key” field and click the “Save Changes” button.
Your plugin should now be usable.