Let me start by advising that you post your questions in the most relevant section of the forums, in this case - this would have been the TileList forum: http://www.telerik.com/forums/aspnet-ajax/tilelist.
In order to define which group tiles go to on the server you only need to add them to the desired group. You can find an example of tiles programmatic creation here: http://www.telerik.com/help/aspnet-ajax/tilelist-server-side-programmatic-creation.html. It uses a single group, yet it shows the basics and you can tweak ti to match your needs.
If you do not want your users to be able to move tiles around, you need to disable the Drag-and-drop feature: http://www.telerik.com/help/aspnet-ajax/tilelist-drag-and-drop.html. This is the only thing that lets end users change the control structure.
In case you databind your tiles, you can see how to predefine groups and put tiles in them here: http://www.telerik.com/help/aspnet-ajax/tilelist-databinding-defining-structure.html.
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