To add a new internal user in your installation, simply navigate to Settings–>Manage Staff, and click the + button.
From there, you will be presented with a form at the top of the page, which you can use to select the new user’s role, fill out their information, and optionally select an avatar for them.
Of note among these fields is the "Hourly Rate", which is related to time tracking in the Timers section of Planning. The value that is entered here will automatically be filled for this user whenever they create a new Timer for themselves. If the "set hourly rate as private" is checked for a particular user, that user will not be able to see their own Hourly Rate that has been set for them (either in their profile, or when creating a new Timer). This is useful for instances where you are billing clients a particular amount for a Teammate or Freelancer's work, but don't necessarily want that user to know that billing amount.
Once you click “Add”, the user will be created in your installation, and optionally they will be sent an email notification about their account (if the "Send Welcome Email" box is checked). This email will include a link for them to set their desired password, and enable them to login.