Azure AD Connect is a software tool that is used to connect an existing on-premises environment to Azure AD and it maintains the synchronization of objects from both environments (Users & Computers).
Before we start this tutorial, make sure that you already have an Azure AD tenant setup ahead of time, Check this link from a previous article to see how it's done.
To get started, download the tool from the URL below and then install it on the Primary domain controller in your on-premises environment, also make sure that you are logged in with an account that has Active Directory Domain Administrator permissions.
Then we insert the credentials of the Global administrator of Azure AD as shown below.
On the next page we insert the credentials of the Domain Administrator of our on-premises environment.
Eventually we shall be presented with the sign-in configuration page. If you have a custom domain already setup, then the UPN suffixes will match that of your on-premise environment. For my case, this is a test environment and hence I don't have a publicly registered domain attached to my on-premises Active directory so I will click the check box to continue as it is. Shouldn't be a problem. It can also be done after your domain has been verified by your domain registrar.
Last page should appear as something like this and then click install.
The Installation and synchronization process can take up-to about 5 - 10 minutes depending on the size of Active directory objects that you have in your on-premises environment, so grab yourself a cup of coffee.
From there, we can be able to see our users in the portal. For my case I had only one user and you can confirm that from the source column which shows Windows Server AD on the user Peter Trizzy Matovu.
That's it, we are done connecting our on-premises Active Directory to Azure AD in 5 simple steps.