If someone joined your team or you simply want to create a new user within your team, note that only the administrator(s) of your brand account can do so.
First of all, click on the upper right side of your Stellar page, on your name. Then, click on "Users" and on the Add user button.
You will have to enter the email address and the role (user/administrator) of the person in your brand account. The person will receive an invitation to join your Stellar team.
New users just have to set up their accounts. It is possible that the email goes to the spam folder so make sure you check it. If you still do not receive it, you can log in by introducing the email used to create your account and clicking on "forgot password".
If you have any further questions, do not hesitate to contact us via help@stellar.io