Clicking on a tab or section control in your form will show a Security tab, along with the Settings and Style tabs, in the properties pane. The top portion of the tab displays a drop down of roles that are available. Roles are created by your tenant administrator or automatically imported from your LDAP or Active Directory server. Refer to Manage Roles for the details.
The Role selector in the Security tab is a deprecated feature that will no longer be available in a future release. frevvo recommends using show/hide rules based on {flow.activity.name} is a more reliable method that works in every use case. Show/Hide rules are easily created using the Visual Rule Builder. Refer to this example -Show/Hide Controls and Worklfow Steps.
The lower portion of the Security tab concerns Electronic Signatures and is only relevant for a section control.