Once you have enabled your login in the control panel, you can download the Conversations app to your Android phone.
You can purchase the app via the Google play store or install the frdoid version for free if you have F-Droid installed.
Once installed, you will be given the option to create a conversations.im account for free, or enable your own. You can choose to enable your own account, and enter <username>@mayfirst.org as your "JID" to access your account.