ClientCare isn't providing support on Analysis Workspace yet, while it is in public beta.
It turns out I am only partially right. You can't drop an entire dimension onto a column header yet. That's planned for an upcoming release.
However, you can add specific dimension values as columns. To do this, mouse over the dimension that you want (in the left rail). You should see a right-pointing arrow appear to the right of the dimension name. Click on that. You will see the dimension values, and you can then drag them over as columns.
Sorry for the delayed response on this. You can definitely add dimensions into a column; you should be able to just drag and drop. If you want to add specific values of a dimension, you can also do that by clicking the arrow to the right of the dimension name in the draggable stack on the left, which will produce a list of values for that dimension. The same is true of the built-in date ranges currently available in the draggable stack; we will be adding custom date ranges very soon, which will give you the ability to define your own date ranges for inclusion in a table, rather than relying on our built-in ones.
You can treat the date ranges in aggregate by not adding a granularity to the table. By default, you will get aggregate data for the date range.