[Seaside] Help understanding WATableReport

[LK]

Sorry to be so dense.  I have been  studying the WAMemoryUse example.  
Unfortunately, some of the code is beyond be poor ability to understand. 
I could use a few more hint :) 
for instance:

in #root: 

Do I need to convert my collection of data objects to an array of rows 
and columns? Create variables for each column, and files those from the 
array result?

in #buildTable
    . . .
     rows: sizes keys asSortedCollection;
    . . .
is #sizes the array that holds all the row data. ie. a relation (in 
RDBMS terms)?

what does this code do?

        (WAReportColumn selector: #yourself title: 'Class')

I looks like it retrieves a subset of something. But, where is the data 
coming from? Shouldn't I be seeing a reference to sizes?

Thanks for your patience.
-Larry