Start by checking that the system requirements are met.
Follow the instructions in this video:
Download Easy365Manager and make sure to register your tenant name correctly (your tenant name is the prefix of the ‘.onmicrosoft.com’ domain that was registered during the creation of your Office 365 subscription).
Install Easy365Manager by running the .msi file from the download page. The installer will install the Easy365Manager snap-in in the Active Directory Users & Computers console and download the latest version of the MSOnline module for PowerShell.
Once the installation is completed you must (re)start Active Directory Users & Computers and perform the post-installation configuration.