On the left menu, click "Settings"
Click Team and Add User: 
Fill out the entire form. Make sure you have the user's correct email so they can receive their invitation to join the team. You can assign them as an "Admin" or "Team Member." Then click "Send Invite."
An email will be sent to your new team member welcoming them to your team. They will need to click the button "Click to Set Your Password" which will take them securely to the web site to set their password.
The status for that person will change from "Pending" to "Accepted." They can now log in to Housefolios. Anything done by them will be visible to the other members of your organization.