I want to have a Pagetype where I can add already existing pages.
As many as I want. Also a page can be in several different SummaryPages. Thus many-to-many relation.

And I want to have a nice way of setting the order.

The coolest way would be if I could just drag the pages into order.
Like you can do with the inputs in a user defined form.

Is there a nice and easy way(class, etc.) to realize this dragging ? I'm considering studying the userdefinedform module. But I'd prefer not to (don't have much time)

Or does someone know some concrete files, api sections, etc. , that could enlighten me ??

PS: Only a few days since I know and work with silverstripe.

Thanks for the answer , actually the "sortable objects in the sitetree" has already become a solution strategy for me.
This way I get the Drag and Drop and the possibility to decide the ordering.
Also I can immidiatly see, where the pages are.

Only thing was, I had to make my own virtual page, but this wasn't that hard. So my SummaryPages can have many pages. And the pages can belong to many SummaryPages. Thus I also got my many-many relation, too.