You can view all members in your workspace and invite others from the Workspace Members page. When you click on your profile image on the right top of the app, you'll see your workspace(s) listed there—select the workspace to go to its Workspace Members page.
On this page, you can add more members by clicking on the “Invite Member” button; there, you can assign roles and set their access level while inviting them.
Once you invite them, they will receive an email to access the workspace and register to Zeplin (if they have not signed up yet).
Keep in mind that you can invite more members than the number of seats you’ve paid for in your workspace. When this happens, Zeplin will apply a 7-day grace period to those members. Within the grace period, you can either confirm or revert the changes, or remove the members from the workspace completely. Learn more about the grace period here.
When you upgrade your personal workspace (you can be a Free plan user or a personal plan user like the Starter or Growing Business plans) to the Team or Organization plan, you will become the Owner of a new workspace and all of your existing project members will be added to your workspace as a Reviewer with restricted access. This means they can only access projects and styleguides that they have been invited to and they can only view screens and add comments without accessing technical details—you can change their roles and access levels anytime from the Workspace Members page.
If you create a workspace from scratch, you as the Owner will be the only member shown in your member list first, and you’ll need to add your teammates to collaborate.
Workspace members can have four different roles requiring paid seats: Owner, Admin, Editor and Developer (only available on Organization and Enterprise plans). You can also assign your members the Reviewer role, which is free of charge and does not count as a paid seat.
You can learn more about the details of each role from this article, and how to manage their access levels here.