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. Selecting one or more roles from the list makes a section or tab control in the form visible/invisible based on the role. Required controls in the assigned section or tab will not prevent submission of the form when that section or tab is not visible. For Example, a non-manager employee filling out an Expense Report will not see the section labeled Manager Approval. The roles of Manager and Supervisor have been selected on the Security Tab for the Manager Approval section as shown below. More than one role can be selected by holding down the <CTRL> key and clicking on the desired roles.
In the section, Manager Approval, the checkbox control used by the manager to approve or reject the request, has the required property selected but it will be treated as not required so the employee can submit the form. The Control Security Tab works in conjunction with forms in a flow. See this Leave Approval Workflow Tutorial for more information.
If a section is assigned a role that is deleted by the tenant admin, the section will not be visible to anyone.
The lower portion of the Security tab concerns Electronic Signatures and is only relevant for a section control.