The Table Fragmentation screen can be used via the Database Navigator and the Management & Maintence node. Double clicking the node will show a screen similiar to this one:
Table Fragmentation Screen
As you can see in the above screenshot, there's the possibility to mark tables with a average page density less than the specified value - use the checkboxes at the top of the screen to turn this behaviour on and off.
The "lighting" button attempts to re-create the clustered index for the table, if such an index is not available, a dialog will inform you about this.
For more information about fragmented tables and the values in the Table Fragmentation screen, please check the MS SQL Server documentation.