1. Use the internal WordPress plugin installer to install and activate the plugin.
2. Upon activation, an account for your specific WordPress installation is created. If an account was previously created, that account information is retrieved from the API server.
Your account is linked to your domain. Note that there is a difference between your normal HTTP and SSL-encrypted HTTPS address, so if you have SSL enabled ensure that your server always uses it. If you do not enforce SSL you will encounter account conflicts and MCC might refuse to activate.
You can see your account info by visiting admin > Settings > MyCryptoCheckout.
If the account tab does not show your account info, the problem is usually that your server is blocking requests from external servers. See the troubleshooting doc page for more info.