Go to Options > Restrict Access to grant permissions on pages.
Before applying page permissions
Other permissions types
What are page permissions?
Page permissions are access privileges granted to specified users and groups on a page. Page permissions that can be granted are the same as the roles that can be granted to a contributing (pro) member in the control panel.
Although individual users can be granted permissions on pages, we recommend you grant permissions to groups only (even if the group contains only one user). If a user's access permissions ever should change in the future, changes can be managed as a global, one-time update in the control panel rather than having to hunt down and manually update each page the user was granted permissions on.
When to grant page permissions
If you have semi-private, semi-public, or private pages or sections and want user groups to contribute to your content (draft, edit, manage) on those pages and sections, you MUST assign page permissions. (Global roles assigned in the control panel only apply to Public pages.)
How page permissions affect global group roles
Global group roles are the roles assigned to groups in the control panel. Since groups are always given the highest role awarded (whether assigned through the control panel or on the page), we recommend configuring groups as Viewers in the control panel to avoid inadvertently allowing higher access on a page.