Data Structures Feedback

Message:
Thanks for an informative and interested podcast . I have learned R
alone by reading in Internet, and being able to hear an actual voice
is a refreshing experience.
I'm catching up with the past podcasts and have completed only 3.
However, I have a few questions y data structures.
Some data aggregation functions return a Table class that I don't know
how to use other than printing it. Therefore I have avoided them in
favor of other functions like those in the plyr package.
I have also read things about data.table, regarding it being a
newer/better alternative to dataframe.
Can you talk us about those two data structures?

Thanks!
Eric