On the Permissions tab you can set security for individual actions, thus restricting actions to selected groups of users.
By default, Apply Security has a value of No (that means, all groups have permission to take all actions). This setting appears on the Workflows page as (all groups). You set security by selecting the Yes option and then selecting one or more groups to have permission to take the action.
Consider this example of defining security for an action: When a developer opens an Issue Details page for a bug in the Dev-Ready state, the Cannot Fix action is available. However when a user who is not a developer opens the Issue Details page for the same bug, the action is hidden.