To add a new user to your entity you will need to be an admin and in the "Settings" section of the desired entity as shown below:
Next, you will need to click the "+ Invite User" button in the top right corner of your window. From here a window will display on the right hand asking for the new users name, email, and permission settings as shown below:
After you select the desired permissions and click "Add" the user will receive an email similar to the one below. Note: If the user is an existing Visible user they will be able to accept the invite via email or through the app.