Requisites:

Full documentation: https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-install-prerequisites


Summary

- Download Azure AD Connect (https://www.microsoft.com/en-us/download/details.aspx?id=47594 )
- Azure Subscription
- Add a domain
- The forest must be Windows Server 2003 or higher
- Azure AD must be installed on Windows Server 2008 r2 SP1 or higher
- The server with Azure AD Connect must be installed .NET Framework 4.5.1 or higher and Microsoft PowerShell 3.0 or higher
- Global Administrator account on Azure
- Administrator account for the Local AD
- Open ports on firewall ( https://docs.microsoft.com/en-us/azure/active-directory/hybrid/reference-connect-ports )
- Create UO with test users


An Interesting Article:


https://dirteam.com/sander/2015/12/01/installing-azure-ad-connect-on-windows-server-2008-2008-r2-and-2012/