Security Classes

SPGroup
SPUser
SPRoleAssignment
SPRoleDefinition

Setting Unique Folder Permissions

SPPrincipal principal = userToAdd;
SPFolderCollection submissions = web.GetFolder("Submissions").SubFolders;
SPFolder newFolder = submissions.Add("testfolder");

SPListItem folderItem = newFolder.Item;
folderItem.BreakRoleInheritance(true);
folderItem.Update();
SPRoleAssignment folderRoleAssignment = new SPRoleAssignment(principal); SPRoleAssignmentCollection folderRoleAssignments = folderItem.RoleAssignments; SPRoleDefinitionBindingCollection folderRoleDefBindings = folderRoleAssignment.RoleDefinitionBindings;
folderRoleDefBindings.Add(roleDefinitions["Contribute"]);
folderRoleAssignments.Add(folderRoleAssignment);

Adding User to a SharePoint Group

web.AllowUnsafeUpdates = true;
SPGroup studentsGroup = web.Groups["Students"];
SPUser userToAdd = web.SiteUsers["pilothouse\\testgroup"];
studentsGroup.AddUser(userToAdd);
Response.Write("Added user successfully");