If I interpret you correctly you are talking about the tabs in the left side pane when you go to Admin mode.
When defining Admin plugins in code you decorate your class like this:
[GuiPlugIn(DisplayName="My custom plugin", Area=PlugInArea.AdminMenu, Url ="~/Plugins/MyCustomPlugin.ascx")]
As far as I know it's only possible to place your plugins in the currently supported PluginAreas. Which means you can't define new tabs or sections under each tab.
As of EPiServer 7.1, you can put your plugins in the following places in Admin mode:
[EPiServer.PlugIn.ScheduledPlugIn( DisplayName = "My scheduled job", Description = "A scheduled job", SortIndex=1)]
See more about PluginArea in the SDK http://world.episerver.com/Documentation/Class-library/?documentId=cms/7/3e82ada9-d4b6-1cbe-a392-bb241fff094e
As an alternative to the Admin menu you could add your plugin as a global menu item (next to Dashboard, CMS etc):
Just remember to keep the amount of global menu items to a minimum (avoid overcrowding) and set necessary security to avoid editors messing with tools not meant for them.
YET another possibility, if you're willing to do a dirty hack, is to edit the file C:\Program Files (x86)\EPiServer\CMS\7.0.586.1\Application\UI\CMS\Admin\menu.aspx, which contains markup for the entire Admin menu. You could easily place a link to your plugin here, or add markup to create your own section.
Be warned that this will affect all sites on the same server, though.
Is possible create a sub item look like ["System Configuration", "Property Configuration", "Security", "Tool Settings" ] ?
Is possible create a new Tab look like ["Admin", "Config", "Page Type", "Block Type"] ?