There are a couple of options available for adding users to your Confluence installation. The options do not exclude each other so it's possible to use them all, depending on your installation and how open your Confluence should be to the outside world.
As you are just getting started with Confluence, adding users manually is probably the way you want to go. Adding users is an option only available to Confluence administrators or system administrators.
To add a user, navigate to the Administration Console in Confluence (Administration | Confluence Admin) and select users from the left menu. As shown in the following screenshot, click on the Add Users tab:
The username must be lowercase and unique to Confluence. If your company has a username policy, it's best to use this in Confluence too. If there is no username policy, I like to use
firstname.lastnameas a standard, that is,