I’ve tidied up a previous Introduction to Cassandra presentation with better diagrams and improved explanations. It’s available as Keynote, PDF or plain old web pages. It’s a basic introduction to the way Cassandra works as a clustered system. It covers Partitioning, Replication, Hinted Handoff, Read Repair and Anti Entrophy. It does not cover the data model.
Presentation classic is still here
If you have any questions or suggestions let me know. You can also use it as a starting point if you are creating a Cassandra presentation of your own.